A powerful graphics card that would fit in my case

Have you upgraded the power supply already? If not, you'll be capping the PSU before you have to worry about size of the video card. The 7750 is one of the lowest wattage GPU's, but it'll still draw 55 watts itself, so you'd want at least a 350-380 watt PSU.

Personally, I'd plan on a 400-450 PSU then any of the smaller GPU's should be fine.

I forgot to mention, sorry. Of course I will upgrade the power supply.

Exactly. HP always go with those crappy 300W power supply. If you want a powerful gpu you must change your power supply immidiately. It depends on the gpu you want but if you get 600W you would be fine for almost any card unless you want to sli or crossfire. The last step would be to check if the gpu fits into your case.

- Fastreaction

I can't find anything that would work very well. I suggest you buy a new case, whatever the heck is going on in there is very very bad for airflow, you have no ventilation at the top of the case except through the psu.

You could very easily get a rosewill r101-p-bk and an antec power supply like this one
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
and be in a much better situation and then you could get whatever gpu you want.

Thank you for your help. I will buy a new case if there's no "good" gpu for my case at all. I'll change my question a bit. What's the best gpu that fits in my case? Haha thank you!

PSU - $20 AC/AR - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
GPU - $109 AR - Short HD7750 - http://www.newegg.com/Product/Product.aspx?Item=N82E168...

You don't need a new case. No it isn't ideal, but you aren't generating tons of heat either.

Maybe it is better to ask the OP what he plans to do with the GPU. If you want to play games on high/ultra settings on 1920x1080p you need a good power supply (better than 430W which iknowhowtofixit posted), like 600W.

- Fastreaction

Yeah "gaming" but do you want to play on 1920x1080p and on high/ultra settings or just mid settings..

- Fastreaction

Thank you very much again. but isn't the 7750 about the same in terms of performance as the 545?

I am gonna use it for gaming, forgot to mention that too, sorry.

1080p, and high settings. As I said, I'm looking for the best gpu for my case.

Then definitely get a 600W power supply. I would just advise you to switch cases. That microcase will do you no good. Too small for the high-end gpu's and bad airflow. That HD 7750 will most likely not fit into that micro case.

- Fastreaction

That is a solid PSU. OP could fit an ASUS HD 7750 in his case if he switched out the PSU and made better cable arrangements, and it would cost him less than that Diamond (Never heard of them BTW) card.

I can't find anything that would do 1080p high settings and fit in your current case without some cable management changes. Any other ideas?

Diamond has been around for a long time. They aren't an enthusiast oriented brand, though. The Diamond card also has a 5 year warranty.

Also, there is no reason to go out and buy a "600 watt" power supply for a card that isn't going to use more power than the PCI-E slot offers. The Corsair I linked above will run your system and a graphics card that has one 6-pin PCI-E connector. You do have an exhaust fan at the bottom of your case but it still has poor airflow. Your motherboard layout is also not idea for throwing in a long graphics card, hence limiting your options. It doesn't make sense to throw a bunch of money at a pre-made HP. If you want to spend a bunch of money, sell the HP and build your own computer. If you want to play games at high and ultra settings with a 1920x1080 monitor, the HD7750 will do just fine.

http://www.anandtech.com/bench/Product/535?vs=541

The HD7750 is as powerful as the 550ti, without the space or power requirements. You can also easily overclock to get even more FPS out of it. Despite how "boring" my recommendation is, it is the right one if you intend on keeping that HP. Like I said, if you want to do more, sell the HP and build your own.

right, except that the 7770 costs only 10-15% more and is at least 20% more powerful, providing a much better value scenario.

I have nothing against the HD7770 whatsoever. In fact, this PowerColor model is even shorter than the Diamond HD7750 I linked:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

The point I was trying to make in my prior post was that there is no need for the OP to invent hundreds in pre-built HP.

Thanks everyone, I understand now. Best option is a new case and if I buy a new card that would fit in my case I wouldn't get many more FPS, right? Oh and what are the dimensions of the card that would barely fit?

That HD 7750 cannot do high/ultra settings. You have to put settings down to get better fps... The best you can do is maybe play on mid settings with a lot of settings down. It is correct that you don't need 600W for this GPU but that is for a high end gpu card not a mid gpu card. It is not fun to buy a "new" card and you already have to put a lot of settings down. It depends on the OP. There are a few options out here. Either listen to iknowhowtofixit and get that card (if it suits in your case) and the mentioned power supply and play on mid settings or just change that case and get a 600W power supply with a high end gpu which lets you play on high/ultra with good frame rates. This of course depends on your budget and if you would like to spent that. Another method is actually like iknowhowtofixit said, build a whole new pc since upgrading a pre-build HP is just not worth it. It is not designed for heavy gamers and overclocking etc. Hope this helped you out  

- Fastreaction

Okay, thank you very much!

Well it depends how much you are aiming for really. I'd dig around on the gaming benchmarks a bit to get an idea of what improvements you can expect. I had a quick look and from what I gather the 545 you have is probably around 8800gd 9800gt performance wise, but I'm not that familiar to be honest.

Yes the case is a bit cramped, but most MicroATX are and there are plenty of those about. With moving some cables around you could possibly find something like an AMD 7770 that would fit in (about 7") and that card will only pull around 80W (your current 545 pulls around 70W). The thermals probably wouldn't be much different either, though it would be nice if you were able to squeeze in a fan at the bottom front of that case.

The rest of your system is pretty low power so I don't see the need for 600W power supplies unless you are considering major upgrades to high end expensive video cards like the 200 watters of this world in which case you'd be aiming for larger case.

Depends a bit on what games you want to play and at what resolutions, might be more practical to work back that way. Even big expensive graphics cards aren't running stuff like BF3 at huge frame rates with everything dialled up. I suppose an idea of budget might help too.

If you take one thing away from this entire thread it should be that pre-built PCs from Dell or HP or the like are horrible for gaming (or upgrading to be good at gaming). Unless you start shelling out the cash for an Alienware the PC you get pre-built is probably going to be worth more in scrap metal than for gaming and upgrading those is a pain.

I pieced together my own PC for $1000 and then customized an Alienware with extremely similar hardware and they wanted $2300 for it. There are a few places that'll build PCs for you that don't charge anything close to what it'll cost to get an alienware, but I've found a lot of those are very limited when it comes to a "budget" build.