Programs won't run from desktop except internet explorer. Help!

[Guest]

Before logon page when windows XP is starting up a grey box has been
appearing withnothing but a couple of Chinese/Japanese characters and below a
box to click with OK. X at top right had no effect. At first I just clicked
OK to make it go away and get on to windows but I'm wondering if this is a
virus that has snuck through. Now I do control alt delete which by-passes
this box.

However. Yesterday I noticed that although internet explorer works from the
desktop nothing else does and the little bar at the bottom of the screen
hasn't been there for a while. This message appears when I try to run
anything other than Internet explorer:

This file does not have a program associated with it for performing this
action. Create an association in the Folder Options control panel.

I've tried to do this but not succeeded.

Today I tried to run a scan but couldn't open that then I went to the McAfee
website to download a free virus scan but it wouldn't download.

Have no idea what to do and I have a CV I need to get on with and print off
ASAP so if anyone could help me rescue my computer I would be most grateful!

 

[Guest]

Boot to Safe Mode With Command Prompt (F8 on restart), and run a System
Restore to a date before the error.\

HOW TO Start System Restore Tool from Command Prompt (Q304449):
http://support.microsoft.com/support/kb/articles/q304/4/49.asp