Since it started happening right after you download something through Limewire and since problems opening Task Manager is often caused by malware and since spreading viruses through file-sharing software is a popular pasttime with some, I recommend you run a couple of online virus scans.
Bit Defender is good as are
]Panda and
Housecall.
If the system comes up clean, try a couple of spyware scans.
Spyware Blaster is getting excellent reviews.