Windows Explorer problem

[mxdi]

Not entirely sure what has happened but in the space of an evening, WE is coming up with the "WE has encountered a problem" on the desktop computer.
It wont let me do much on the computer, done virus scan, picking up nothing.
Any ideas or things I could try to find out the problem?
Not sure if its related but we have set up wireless this week on the 2 computers, laptop is fine though, they are not networked.
TIA

[arcturus]

Can you give a bit more info, such as what is the full error message and when does it appear.