[grim_squeaker_x]

As a number of people said, it probably is that your computer tries to do too many actions at once, try closing a few messaging programs (I.E. ICQ, AIM etc.), that might help, if this doesn't work try closing all programs in the background using control alt delete except the following programs:
Explorer
Systray
Virus scanner (Always should be enabled while you are online)
Firewall (If you have one)