Dude...
Although it is possible that your HDD is crapping out, I'd try disabling all of your startup apps, and I'm not only talking about your startup folder.

There is a utility called startup.cpl ( http://www.softpedia.com/public/cat/13/7/13-7-9.shtml )
run it and disable everything. If it solves your issue go back and restore one item at a time till you find the app.

I'd also go into your BIOS or Hardware setup page (del or F2 after power up) and reset to defaults with the new card removed from the PC.
Did your machine come with onboard video? If you are adding a AGP/PCI card to a machine with shared video, you might have to disable that controler in the BIOS.

This sounds more like a software/config issue than hardware.

Good Luck!

j.

96 LX 3.0L MTX - Black/Tan K&N; 12lb F/W & uprated clutch 2.5" Pipe; SVT bits; Mystery Mod; Pull-tie Mod; UN-tuned Mod; 3rd Gear Synro-Crunch Mod 280K on the Shell, and 40ish on the Motor... 1/4 mile?? Yeah, it's a fun daily driver...