Windows Explorer Has Stopped

When Vista starts I get a message that 'windows explorer has stopped working,
if I cancel, start-up continues, unexpected lock-ups occur, if I allow it to
go through its process it continues in a redundant search for an answer,
restart and sending info to microsoft.....

Is there a fix or answer?

Upon entering Vista desktop, the message is 'windows explorer has stopped, if
I cancel it restarts and i seem to be good to go for a while until it
crashes, usually very quickly, if i let it take its course it goes into a
redundant, checking for an answer, restarting, sending info to microsoft over
and over again.....

Is there a fix or answer?

I find also that it's extremely slow...