The First Question Of Troubleshooting: what changed between the time
things worked and the time they didn't?

The Second Question of Windows Troubleshooting: what is the
malware/virus status of the machine? If you think it is clean, what
programs (and versions) did you use to determine this?

Be sure the computer is clean:
http://www.elephantboycomputers.com/page2.html#Removing_Malware

If the machine is clean and since the change was sudden, if you can't
pinpoint what is different (First Question of T-shooting), then try a
System Restore to when things worked.

Start>Programs>Accessories>System Tools>System Restore
"Restore my computer to an earlier time".

Malke