I have been servicing this client for several years. He got his computer initially from a local shop. Generic system

Ever since he got it he has been complaining about random lockups. Thats before I started working with him. Several years ago

Forget the old system, this is what it is now, not what it was before:

I replaced the moterboard with a ASUS CLUS2C motherboard
replaced the memory and the CPU and the fan with the new motherboard
Replaced the power supply
replaced the hard drive
replaced the zip drive

Client always had a TBU but we replaced it with an 8.4 gig TBU

It still locked up at random

The old mbd cpu and memory works fine in another case. Remember, I replaced the power supply 350 watt The other case has a 300

Ohh and I replaced the video card too

I have replaced everything but the cdrom drive, the floppy and the case. I have formatted this system so many times that I can do it in my sleep. This is a business system. We are not talking user error here. And all the data has to be restored intact

It locks up.

I built him a new system just like his home one and it works fine

Anybody got a clue? why the system is locking up afer replacing everything? My instinct is telling me that it is the case somehow