Just replaced mobo, graphics card and power supply with MSI P6NGM and pentium dual core 3.0 (8400), GEForce 9500, and 2 gig RAM. Remarkably old hard drive (ATA) with old operating system XP pro started up first time and apart from loading board drivers, graphics drivers etc was fine. Added a 500 gig SATA drive and cloned operating system onto it with Seagate tools. Removed original hard drive and with partition magic, resized partitions on new SATA drive. All fine until I added an ATA hard drive used recently from which I wanted to transfer some old files. Went wrong from here it seems. On start up desktop loads and then soon after get message to say Windows explorer shut down to prevent damage to PC. Removed the ATA hard drive and still the same. Put in old hard drive with XP on it and still the same. Once explorer shuts down nothing works apps or task manager. Is this a software or hardware fault? Any ideas gratefully received.