Random BSOD after reinstalling nvidia graphics card

Hello,

Since the past 6 months i have been using my PC using my onboard graphics which is HD4200 (must be ATI), but prior to that i used to have my GTX 460 installed in this PC but it was on a 32 bit windows 7.

On 6th Sept 2012 i re fitted my GTX 460 with the latest drivers of that day ( first i uninstalled the ATI drivers from device manager and then used driver sweeper in safe mode) but soon after installing the GTX in 5 minutes got a BSOD but all i could see was a percentage counter like 0-5-10-15... 100 and a reboot. All this happened in 5 seconds max i guess. I reformatted the PC and this time installed the previous WHQL drivers from nvidia namely 295.xx something but they didnt work either.

All i had left to do was to remove the GPU and reinstall the onboard drivers and without my gpu pc worked great.

On the 18th i retried the experiment and it worked for 2 hours, even played heavy game on it and used the PC as i normally do and had no issues. But after 2 hours not even playing just seeing some images on HDD and bang another BSOD. SO i removed the GTX once again and its been working fine on onboard graphics since then. This GTX had been working very good for the past 2 years without a single crash or anything and then i simply removed it and kept it safely. Only thing between this was a shift to 64 bit OS, all things other than that are still same. I have explained the story as best as i could and i am still OK with my onboard chip but want to play some games as well in spare time but why this BSOD is beyond me, hence i come to you fine people for some help. The dumps have been attached as the forum asks for.

Also if its important or not but nothing in my system has been overclocked or tempered with.

Thank you for a prompt reply. So for this driver verifier do i have to reinstall the GTX 460 and make the system i mean "less stable". Sorry for all this but im not that much into computer hardware so i asked.