Okay so I've just installed a new graphics card (HD5770) and the computer is now acting odd.
When I press the power button, it powers up and then tries to use the DVD, resets and tries to use the DVD about five times. Only then does it start booting normally, at which point the monitor turns on etc.
Go to your BIOS and disable "Flopy disk drive", and check if it helps.
Also how many HDD's do you have ?
Yes,if i remember right, in another thread the OP mentioned he had a Nvidia card before it.
I was going to post it, but i wasn't sure if it helps or not, but here is how to do a clean install of drivers(since you moved from ATI to Nvidia,its recommended to do a clean install)
1_Download and install "Driver sweeper" from Guru3d.com and install
2_Go to add/remove programs and uninstall the driver and reboot
3_Boot to safe mode and open driver sweeper,then click on Nvidia and then click on clean
4_Reboot and boot normally to windows and install the new drivers after that you need to restart,and its done
saint - yes I had an 8500GT. I did uninstall the old drivers before installing the new ones, but I didn't use anything like the 'driver sweeper' program.
Maziar - I've already disabled the floppy drive in Bios, otherwise it tries to install a floppy drive that doesn't exist :-). Also I'm running an old 250GB IDE, a WD 'blue' (I think) 160GB, and a WD 'green' 1.5TB.
As for your next question, I'm running a Thermaltake Toughpower QFan 650W PSU.
Alright I tried driver sweeper - it nearly destroyed my system.
I used it, restarted - suddenly Windows 7 refuses to start, even in safe mode. After over a day or trying to get it working and involving cannibalising another computer, I'm finally back up, but only after both my backup harddrive and 1.5TB games hard drive were screwed up so badly they both had to be formatted again.