Unexplained Daily Lockup

I have a user that on a daily basis locks up his laptop (Dell Cpi with Win 98 SE with 64k mem and 266 Processor on a Novell Network)This happens once a day after booting up within 40 minutes of logging on and doesnt happen again till the next morning.
There are no unusual APs running, Nothing timed to run. It is a normally used image for us. The laptop has been poured over and the all networking issues redone.
I have reimaged it twice in futile attempts to fix this. His log on scripts havebeen rewritten, I have switched the Hardrive and
network card into an different but identical laptop. Everything has essentially changed except the problem. Help! At least this guy is being cool.