Hey I got a question.....

Every time I start up limewire and start downloading then after 5 minutes my omputer will restart Iam getting sick of it

PLEASE can anybody help meeeeee????????????????????????

My specs are.
amd 64 4000+
asus sli deluxe (nforce 4 chip)
2gb ram
250 GB
asus geforce 7900GTX

Please help me !!!!!!!