House to Office connection. Need advice and direction....and HELP!

Sounds like a few potential issues. Likely the powerline adapters are a big part of the reason. Iknowhowtofixit's suggestion is going to be the easiest way to fix the connection. Assuming you cant just move the router upstairs or bury a cable out to your office or any of the other hardware is outside your price range, try testing out your hardware. Here's a bit of a drawn out to test it bit by bit to find your weak link.

1. Have you connected directly to the modem with a computer (laptop or otherwise)? Before trying to trouble shoot a whole slew of potential issues with your own network make sure the source is running how it should. Once you're plugged directly in to the modem, run a speed test. Most ISP's will have some sort of portal but if not www.speedtest.net is a good site to use to test. Once you know if your direct feed is giving you the speeds you should be getting you can start checking your network piece by piece to see where the fault is.

2. Assuming you've confirmed your speed from the modem is what you're paying for, lets figure out your powerline situation. TP makes good powerline adapters in general but realize all powerline adapters lie horribly about their real life speeds. Plug one in to your modem and then go to the garage and put the other powerline adapter where you'd want it. Plug in directly to that powerline in the garage and run a speed test. This is likely you're biggest weak link. If you've had to jump any circuits in your circuit breaker between your basement and your garage you will lose substantial speed. Also depending on which plug you use in the garage, your speeds will vary. It's just the nature of Homeplug AV powerline tech. Also make sure that you're not sharing the plug that the powerline adapter is using with anything else. Anything that causes noise on the line (fans are oddly horrible at this) is going to cause a decrease in performance. If you're finding that you're speeds coming out of the powerline adapter are the weak link consider returning them and picking up a better pair of AV2 powerline adapters. I recommend the ZyXEL PLA5405KIT or better yet, if you can find them, Comtrend PG-9172-Kit. The Comtrend use G.hn technology instead of HomePlug AV2 and aren't as sensitive to line noise or circuit breaker nonsense. But they are harder to find and the G.hn tech isn't really widely used, tho that may change soon.

3. Assuming your powerline works at an acceptable level, plug the Cisco E1000 in to the powerline adapter. Plug in to the router and do the speed test. Routers eventually die and yours could just be on its last legs so its good to test hardwired before dealing with the nebulous hassle that is wifi. Assuming it works well, switch out to a wireless device and start testing your wifi speed off just the router. If walking around with a laptop is unrealistic there are as bunch of wifi strength meters available for android and ios. If you aren't getting speeds that you want, I would highly recommend getting a router where you can hook in a directional antenna. If its only servicing your office, theres no sense trying to beam the signal everywhere. But you'll need a new router with external antenna for that. Not hard to find and a simple search on newegg will find you a directional antenna.

4. Assuming your wifi is coming out how you want it, set up your TPLink WA5210g and test your speeds from there.

Somewhere along these tests your weak link should show itself. Once you know whats happening and why you can look for a real solution that fits your needs and price range.

azaran he needs to replace the repeater it an old g unit. the e1000 is a n unit. so he losing max speed from the router to the repeter. he want to put a n or faster in the place of the g repeater.

I totally missed that whole G unit thing. He should still be getting better than 3-5Mbps but yeah that is a definite upgrade for better speeds.

xcoyote with wifi now there to bands now 5g and the older 2.4g. the 5g radios are made for shorter range but more data. a lot of the newer routers are combo units that let you bond both radios.
http://www.linksys.com/us/p/P-EA6900/
you pay a lot for the faster wifi routers that are out now.
on the n routers there three speeds of them.
n600/n300/n150.
if your looking to save some money look for the n600 units. any new routers will let older g/b units connect. they just connect and move data at a slower rate.
http://www.amazon.com/NETGEAR-N600-Wi-Fi-Router-WNDR3400/dp/B0041LYY6K
https://www.trendnet.com/products/wifi/N-access-points/N600/TEW-753DAP
set the ac point up to connect to the newer router for max n speed.
http://www.newegg.com/Product/Product.aspx?Item=N82E16833156495
http://www.newegg.com/Product/Product.aspx?Item=N82E16833156474

Sound like you're wifi is the big weak link. There are a ton of wireless router and access point options out there, so really its going to be budget dependent more than anything else to make a suggestion. Given your rapid drop off in speeds, in addition to upgrading the WA5210G, I'd look at upgrading your router to one with external antenna. Going with that option will give you the ability to use either high gain omni or directional antenna. That combined with one of the high gain access points your looking at should give you as good a speed as you can get with your current setup.

As for the powerline gear, try playing with which electrical socket its plugged in to if you can. When I did my setup in my house I had huge differences in the same room depending on which plug I was running from.

looks good those two units. should work fine for you for years. if you can look at newer uints with two 2.4g radios or 2.4 and 5g radio. if the 5g are in range of each other you get better speed. whe nthe cost comes down then look at 5g or it replacment.

check the back of the pc make sure there two led on the network port one amber that shows it linked and a green one that blinking. if not check to see if there something in the port blocking the cable.