this happens to me all the time, but my pc is only running at 1.2 gzh, with 512 ram as well.

there are several solutions to this that work for me.
1 = close everything including limewire and run ad aware and defrag aswell. this is the main problem with limewire i find, is its ability to completely fragment your hard drive. and it often collects alot of malwares.
2= check in task manager to see if anything else is going on, normally you can spot what shouldnt be running right off the bat.

this works fo me, when it happens, that fixes it.
now you can run it again.

also, you may want to slightly decrease your upload slots as the more people are uploading from you, the more it will use up your cpu usage and bandwidth.

any other questions, email me at benbakerzzn@hotmail.com