What is the model you have exactly and did it run without a sd card at one point?
When TT detects an application on a sd card, it attempts to boot from it. If you can get the application back on the unit and your unit runs without an sd card, we may be able to resolve the issue.
I can't imagine that any map you had was on the sd card if the card is indeed only 128 megs in size, though.
Have you downloaded an updated map? If so, it's sitting on the computer here:
C:\Documents and Settings\yourname\My Documents\TomTom\HOME\Downloads\complete\maps\
in a compressed form.
So, in summary:
If your unit can run without an sd card and if you have a downloaded map in compressed form, then we can probably fix the problem.
If you do NOT have the map update and you do NOT have a current map backed up, then there is a problem ..