NT fails to boot intermittently

I support a client with a Windows NT Workstation that fails to boot properly every fifth or sixth time the systems is started. When the initial blue screen appears at boot showing the servive pack revision and the sequence of dots all seems well until the screen goes black and the same blue screen reappears – except this time the system is locked up. I can’t seem to find a solution. The problem is intermittent and rebooting after the failed boot is always successful….until a few boots later it happens again. Otherwise the system runs perfectly and 75-90% of all boots are successful. Could the machine possibly have bad memory or another hardware problem? It seems awfully early in the boot sequence for software to be causing this problem.