A little more information would be helpful.

Machine Type and CPU
Operating system and sp
HDD
RAM
Firewalls
LimeWire Version
Java Version
modem type & model no.
connection type (ADSL,DSL,Cable,Dialup)

I just upgraded to LimeWire Pro 4.4.3 with no problems.

You might also try defraging your hard drive. (Maint. that should be done routinely to keep your computer healthy)

If the fixes LotR suggested didn't work try uninstalling from add or remove programs and reinstalling.