AV, Malwarebytes, Hijack this, IE & FF won't run

[lithodora]

The computer in question is my fathers. It is one of the little 8" Acer computers running Windows XP SP 3.

Avast Free is the anti-virus. The computer was brought to me when he was unable to get to his Yahoo mail from his Yahoo Messenger.

Ok, I have no idea what he did or has run to get to this state. I can tell you 1) Yahoo & MSN Messengers work 2) Firefox never loads 3) IE loads but becomes unresponsive immediately. The crash report suggests a fix, but since it loads in IE I can't view the thing.

Running AVAST gets:

Windows cannot access the specified device, path, or file. You may not have the appropriate permissions to access the item.

Booting in Safemode with Networking I was able to get installers for HijackThis and Malwarebytes' Anti-Malware onto the computer. Both installed without issues.

Loading them however:

Windows cannot access the specified device, path, or file. You may not have the appropriate permissions to access the item.

The case with Malwarebytes' AM is that it loads and begins to scan for 4 seconds then closes. After that the message above is given when trying to open the program.

While in normal mode there were two processes that stood out to me: b.exe and msb.exe

At this point I am unsure how to proceed and would appreciate help. Thanks.

[lithodora]

Combofix fixed it.