Did you send a payment reminder?  If they don't 
contact me within three days I usually send one 
out.  I've had several people e-mail me 
immediately to say they'd forgotten.

Once it's been seven days(I think) you can file 
a Non Paying Bidder form and e-Bay will send the 
person a warning, asking them to pay you.  You 
have ten days to work it out with the person, 
then you can file for a Final Value Credit and e-
bay will give the person a Non Paying Bidder 
warning.  After the third incident they're 
placed on suspension.

You can also request their contact information 
from e-bay (phone number, mailing address) just 
in case their computer is down.  There's a link 
to the request form in the Non Paying Bidder 
section at the bottom of your Selling page.

Why do I know this?  I just had to do it to some 
jerk who won't pay me!  Now I have to re-list a 
whole LOAD of Star Trek hallmark ornaments.  It 
sucks to get burned on one auction, but it 
REALLY sucks to get burned on several by the 
same person at the same time.

Hope this helps!  I'm sorry you have to deal 
with that crap.  If it helps, I totally feel 
your pain!