Buying a new graphics card

You will likely need to upgrade your PSU first, according to dell you only have a 375W unit in the XPS 420. If you want to avoid needing to upgrade your PSU something like a 5770 would fit your budget and wont use much power so you could run it on a lower level PSU like that.

Your power supply is what will limit your choice of video cards. Your system usually comes with a 375w PSU. I would recommend an HD5770. It will be approximately 50% faster than your 8800GT and give you DX11 compatibility while using the same amount of power. They can be found for as low as £120;
http://www.ebuyer.com/product/189239

like the others have stated, get the ATI 5770. no need to upgrade your PSU then

^+1

Thanks a load all of you guys. Also one last question: Is it sure that its just my graphics card thats broken? Because its still in my PC and Windows have stopped it running because it malfunctioned, yet I can still use this PC but cant adjust resolution (At least havnt seen anywhere to do so) and there are grey columns on the screen; is this just how bad my motherboard graphics card is?

Thanks a lot for your help, will start looking up 5770's now. Also if its not much of a hassle are there any other bettergraphics cards that would fit my PC well but for a larger price? Say £200> was just wondering in case I can spend more. THanks.

Also, (Wouldnt let me edit my post); ATI CrossFireX and others that require my motherboard to be ready for them, are they worth it? And will my motherboard be able to work them? As all my PC has had is that 8800GT I dont know how it would react to an ATI lol. Thanks

To adjust the resolution you will need real drivers for whatever graphics adapter you are using. No, "grey columns" certainly aren't normal.
You would need a new power supply for a card better than the HD5770.
I don't understand your question in the last post.

Sorry, basically will the 5770 definitely work for my PC? My PC has less wattage than it recommends but many say that its fine, and that it doesnt use nearly as much as the manufactururs say it does, and many who have XPS420's like mine and have the 5770 say its fine. Nevermind about the corssfire question lol. Going to buy the 5770 tomorow (UK time) so any confirmation that 5770 will definitely work, or any info about what could go wrong would be a lot of help within the next 20 hours. Thanks.

The HD5770 actually uses slightly less power than your 8800GT so that shouldn't be a concern.

^+1 you will be happy with the 5770 and dx11, also you could (if you have 2 pci express slots) throw in the 8800gt and use it as a physx card later on.

Alright thanks all people that have helped, going to buy a 5770 today   now for the new-to-me task of installing it D: how do I know if I have 2 PCI slots? Will there just be a spare one next to where my broken gcard is? And what does having a 2nd graphics card do to help your pc, and could I run them both on my pc because Im sure 2 gcards would go over my wattage limit lol. Thanks both of you.

HD 5770 is cheap and good and also in your price range. But if you want a higher end card and more future proof go for GTX 460 1gb. It costs 230 bucks or so though

He was talking about using the 8800GT for GPU accelerated physics in the handful of games that use the Nvidia Physx API. Not nearly worth the hassle IMO and yes, you would need a new PSU.

Alright cool, yeah the 460 is out of my price range   thanks for the suggestion though, will keep it in mind for future graphics cards. So is this pretty much solved; the 5770 will definitely work on my PC and be better than the 8800GT which broke? Thanks to all for advice.

Yeah, the HD5770 should be fine and like I said earlier it should be roughly 50% faster.

Thanks all, should be delivered here tomorow  

Some have said I should get a PSU; I would like to get one, on NewEgg it says I need about 430 watts in total for my pc, so looking for about 500-800 watt PSU. Any advice on where/what to get? Im in the UK so cant buy from newegg

Once again the HD5770 uses less power than your 8800GT. The power supply cannot possibly be able to handle one and not the other. The people who are suggesting you need a new one do not understand how Dell rates their power supplies.

Weird, many are saying to get a better PSU, some definitely, some just in case, and many are also saying it will work fine. I'm gonna get a 650w PSU just in case, and to provide room for any extra upgrades I might like in the future. Is this a good choice? And should I install the PSU before the graphics card, or can I use the graphics card for a bit before installing the PSU with no harm done?

Is the CiT 650U compatible with the 5770? This is the PSU I might get; need a fairly cheap one. Thanks

Apparently the CiT 650 is awful. Can anyone reccommend any PSU's for under £60 that are compatible with the 5770? Thanks

Ive had a look at some, and a couple catch my eye; OCZ StealthExtreme 600w, CoolerMaster Real Power M620w, and the Corsair Tx750w. They are all around £50-£70. Which is the best for me? Thanks, and if you have any other PSU's in mind that are better and around/less then the price, please tell, thanks.

DELL sold the ATI 4850 with that same PSU. It's plenty powerful for the ATI 5770.

if you really want a replacement, and you don't, these PSU are fine and in your budget

corsair 400w
http://www.ebuyer.com/product/150985

antec 430w
http://www.ebuyer.com/product/120376

corsair 450w, more headroom...a lot more
http://www.ebuyer.com/product/131052

the OCZ is average

the CM makes a fine door stop and paper weight

the Corsair is excellent but far more power then you will ever need

I don't see anyone telling you you need a new PSU. I don't know why you would come ask for advice then after everyone tells you the same thing ignore it. Seriously, it uses less power than your current card. This is a fact, you can look it up. It's why we recommended the card in the first place.

I think what Dan's trying to say is he's afraid that the new GPU will also broke down because of the old PSU failure. It is possible that this scenario to happen, since PSU component's aging could affect its efficiency. But then again, this will only likely to occur on a 5 year old PSU, assuming it's a first grade PSU which is used under normal conditions.

That's why, Dan decided to get a new one for reassurance. Wouldn't be funny to found out that a new GPU faulted on the first try just because of a cheaper-than-the-GPU-component is busted. I can understand his reasons.

It is always better to have a higher quality and capacity PSU above your system requirements. But money wise, it's not recommended.

As a computer addict (a friend of mine) once said, value is the highest ratio between price and performance. In reality, an 80% performance with a price of $50 is better than a 100% with a price of $90 . If you only need the 80%, why go for the 100%?

But the decision is yours to make, we're just here to help you decide

The card should be coming today. Any problems and I will say, I'm going to try install it as about 70% of people say it should be fine, if not I can send it back I guess. Will still think about a PSU not because of the card but because I may, and probably will, want to upgrade my PC some more in the future. Thanks to all who have took their time to help.