I recently had some problems with a bad PSU, and I stripped down the system to just run with mobo, RAM, CPU & GPU to find the problem (didn't know which part was faulty). I got a new PSU, installed everything, and booted. While POSTing the lights on the keyboard go on and out (which is normal), but when it says "press DEL to enter BIOS setup" it has already stopped working. It goes on booting into Windows where I found out the mouse doesn't work either. When I plug the keyboard out (whilst in Windows) and then back in, the PC gives one short beep. (it does not do this for the mouse, however). After the beep it still does not respond, though. There was a "found new hardware" dialog open, but I don't know what it was for, and since I can't use any of the peripherals (mouse & keyboard) I can't install it either. So then I tried clearing the CMOS (I have an MSI K8N Diamond Plus with a handy red button ). When I boot, it gives me a screen that says "CMOS Checksum Bad". Accompanied with my obvious swearing and cursing, it gave me two options: either go into setup or load the system defaults. But the keyboard doesn't work so I'm stuck! So yeah after five weeks without PC I finally get it to boot and then this happens. Please help me out.