Earlier that day I had upgraded the programme when it asked.
At the end of the day I right clicked on the Limewire icon in the System tray (as I always do before shutting the computer down) and exited (I think) the programme.
As the programme was shutting down a window flashed onto the screen saying "unistalled" - but was only displayed for a second or so, and unable to be fully read. I then shut the computer down.
The next day the icon was gone from the background, and the programme gone from the "Program Files" folder.
Is there any way to get it back, without a fresh installation. (I had 15 downloads partially completed).

Which security programs are you using? Some antispyware will see LW as a threat & delete the .exe (eg PestPatrol).
Have you upgraded/updated any security programs before this happened?
Limewire keeps disappearing! I have to then reinstall! help!!!

When I right click on the LW icon in the system tray, the options are Restore, About, Exit after Transfers & Exit.

Check your security programs and their settings