Lag on games after graphics card upgrade..

[dopeknight]

Until a month ago I was using Zotac GT 210 graphics card which was descent enough to run TeamFortress2, Minecraft, and few other games and I was using Windows XP.
To upgrade it I bought The Sapphire AMD/ATI Radeon HD 6670 1 GB DDR3 Graphics Card Sapphire AMD/ATI Radeon HD 6670 1 GB DDR3 Graphics Card | Graphics Card | Flipkart.com
So with it I put Windows 7 also, (GT 210 was a temporary card, I had a 7300GT before and was using on-board also for a year or so when the 7300GT had burnt out and all that time I had windows 7. So for time being I had bought the 210 which had problems with windows 7 so I was using Windows XP.) and it was working good enough that I could play MW3 in low graphics, tf2 and few other games at descent FPS.
Other Specs: Intel Q6600 quad core @ 2.4Ghz / 3 GB RAM/ Windows 7 Ultimate/ Mobo DG31PR/ DX11.

And until a week ago, something happened and every game started lagging, I get around 40FPS on minecraft and on servers its like reaching 10FPS.
TeamFortress 2 which was working smoothly, now has lag when viewing long distance. I re-installed Windows 7 its still the same. Even Ubuntu for some reason lags and then goes blank..
Also I added an extra hdd of 500GB about the same time all this started but I thought that doesn't affect anything much right. ?
Can you guys point me at anything that I should be looking at ??

[sam]

which psu are you using? remove GPU and install it again. though unlikely, are you using latest driver?

[Bodhisatwa]

Install latest ati driver..

[dopeknight]

I installed the latest driver too.. I gave update on Catalyst and it says its up to date.. I'm using a Frontech 450W PSU, the gfx card needs only 400W na.
Actually to think of it, windows 7 used to lag a lot, like framing when I was using 210 so I switched to Windows XP.
I did remove and install the graphics card again, I used the onboard graphics and it worked well but no game works on it, so using the 6670 is better but its not as good as before, something has changed..
Will download Windows XP now and try installing it tomorrow again and post the results.

[sam]

if windows xp doesn't solve the problem, throw out the PSU.