You can eliminate any errors that could be bios related by resetting the bios, just unhook the power cable and remove the battery for a couple of minutes put it back and go into bios and load the optimised defaults if you have them and set your boot priorities again, i dont think it will really solve to much but its a good place to start to eliminate an errant setting causing it.
Your C drive seems Quite small which makes me thing its an older drive than the others, what i would do is get your newest or fastest drive back up everything you want to keep and do a fresh windows install on that drive you should always have your windows installation on your fastest hard drive as the speed of the drive directly affects system performance, its seems to me the easiest way to eliminate a problem with the installation/drivers etc and the hard drive which i have a sneaking suspicion is on its last leg. You can check the drives condition using manufacturers diagnostic software but given the size im guessing youve had the drive a few years and they do have a lifetime so it would be approaching it if its older.
Theres a lot of half measures and tests but given you have multiple drives i would install windows on one of those and wipe the other drive clean, reinstallation doesnt take to long and of you go on the internet and download the drivers you need before hand go on
Your mainboard drivers i think are here http://support.asus....SLanguage=en-us
but there are a few different boards i cant find one with the nforce audio though they are all realtek audio or dont have audio drivers youll need to loo in your own manual or on the board to get your specific board some have better support than others. ATI will have a driver for your 7500 if you dont have one, once youve got your drivers together burn them to a disk and keep them they are something you should have lying around. That will eliminate the problems hopefull if it doesnt you can always go back to your old installation. As long as you back up the stuff you keep this should be a safe and quick operation and relativley simple, alot of people do it regularly as a clean windows install has its advantages.