Having 5 Fans installed does not guarantee that you are not going to have any thermal issues. Especially how air circulates in and out, so might as well check any temps going high. You might wanna recall any recent changes, updates to hardware and software you have added that can give you sudden shutdown or lagging. Any corrupted, incompatible programs, protection softwares installed might also cause this. So uninstalling some and using basic protection antivirus and windows firewall will help you trim down the problem. You could also try running into Safemode to check on the problem and try look for reinstalling and or updating drivers for certain fixes address to your issue. Testing RAM modules by using one alternately on slots while booting can also help in troubleshooting the shutdown problem. You could also use chkdsk /r for any system error and will try to repair them using your XP CD.
