Firstly, which AV program are you using? Make sure that you keep it updated & scan your computer regularly. You should also scan all files that you've downloaded, before you open them. Have you run an AV scan recently?? We can't guess whether you have a virus ...you have to scan your computer with a good, updated AV to find that out

Here are some good, free security programs. Click on the link below.
http://www.gnutellaforums.com/264170-post2.html

Check out this thread below for info about online AV scans.
WARNING: Viruses on the network you should be aware of

Some people have had problems with LW not loading, after updating to Java 1.6.0_01. If that's the version you're using, try this one instead. Use the JRE offline installer & remove any old Java versions before installing this one.
Java SE Downloads
If that version seems on good, you could try this earlier one. Again, remove your old Java version before installing a new one.
Archive: Download Java 2 Platform Standard Edition (J2SE) 5.0 Update 11

Otherwise, delete LW's preferences folder when LW's properly closed. See point 3 here & also point 2 if you've used older versions of LW in the past (there could be a folder in either location).
Fixes for LimeWire
This will kill all of your settings within options, you'll have to go back through afterwards & reset things. If you're not sure of your settings, go through LW's tools > options & write them all down, so that you can reset things later.

Also try changing compatibility (point 5 in the 'fixes' thread).