experiencing some serious issues. My pc has been
working fine for months - until now.
At midnight my AVG (free version) started running its
daily scan and I went to sleep. In the morning, I
went to my pc to power it down and noticed an error
which I should have written down exactly but it
resembles this: "Cannot create file D:\$n"
Explorer was visible and everything _looked_ fine, but
I was unable to activate "My Computer" and I also
could not reboot from Explorer... both functions
simply timed out.
I forced a power off by holding down the power button.
When I tried to reboot, I got past the BIOS but after
that windows never loaded. I observed that all the
hard drive lights were on, and the green monitor light
was on, but nothing more. I did not hear any unusual
sounds from the hard drives.
If anyone has any ideas how to troubleshoot this I'd
much appreciate it!

What are the computer specifications? Make/Model/Ram/CPU and so forth

Have you tried Safe Mode?

You said after it got past the BIOS windows never loaded. What is actually on the screen? Do you see a cursor?

Why? Was the system froze up? Didn't CRT+ALT+DEL work?