Crash after s/w re-install & h/w change

Help!! A customers PC keeps ‘freezing’ for no apparent reason. The system is built on a Gigabyte GA-7ZX m/b with Athlon 1G CPU and big fan. 2 x 128Mb PC133 memory, Diamong Supra Express 56I Pro internal, Creative Riva TNT2 M64 32Mb AGP video, Mitsumi CD-burner and a DVD rom. H/D is 30Mb Maxtor.

System has had a complete h/w change. W98SE loads fine, all drivers okay, Office 2000 ok. Client loads Pipex ISP s/w and Norton Antivrus.

Everything fine, then system just freezes: No blue screen, no warning – just frozen. Need to re-boot to carry on.

Scandisk no probs, memory checked out okay. CPU & system temperature okay.

What can anybody suggest about this particular s/w and h/w configuration?