Try deleting LW's preferences folder when LW's properly closed. See point 3 here & also point 2...depending which version of LW you're using, there could be a folder in either location.
Fixes for LimeWire
This will change all of your settings within options...go back through tools > options & reset everything to the way you like it.

If that doesn't fix things, have a look in the thread below (mainly the first few posts by Murasame) for info about maximising LW's performance
A few things to consider while configuring Limewire for optimal performance...

If you're using basic & see a turbocharged connection (blue bars), it means that you're connecting as an ultrapeer rather than a leaf. The network will choose you to run as an ultrapeer if the network needs UPs at the time & if there's no firewall interfering with your LW's performance. For more info about this, use the forum search to look for ultrapeer