Disk Read error - CTL ALT DEL and other performance issues.

I had major problems with Windows VISTA and installed Windows 7 as a fix. Problems persist, in no particular order;

a) when booting, I get the dreaded Disk Read Error - CTL ALT DEL and I cannot escape it.
b) My disk drives won't read my install disk, even if I alter the boot sequence in BIOS, so I can't boot from disk and reinstall
c) Restore points are always being wiped after I do eventually manage to get it going
d) Sometimes when I reboot it takes me to a screen offering a variety of boot methods, but I can't start in safe mode
e) pressing f8 to boot in safe mode never works
e) I have checked my hard drive with the WD checking download...it seems fine
f) I have run C CLeaner...no problems.
g) sometimes the only solution is to leave it turned off overnight
h) I am frightened to shut it down because it will probably not reboot!

Any ideas, anyone. The problems tend to manifest themselves in different ways, and there is no consistency in how and when the problems start. The hard drive seems ok. When the PC works (as it does right now) it is great, so the OS seems fine too.

Any help gratefully received

Thanks Rich,

I have had this at the back of my mind for a while now...thing is, this is quite a new Hard Drive. It was installed because the old one was also playing up. If it is the hard drive, is it possible for it to work fine (as it is now) and then fall over from time to time (and then start working fine again)? Not an expert on these matters....

Alternatively should I consider opening it up and jiggling all the cables to ensure they are properly seated (that's a technical expression by the way..)