Hi, I have an older PC which I gave to my mum. It originally ran Vista, but I bought and installed Windows 7 Ultimate around 6 weeks ago after it had been inactive for 3/4 months. It was running great, but a couple of weeks ago it just started hanging for no real reason. Also, at startup it would say that the computer had not been shut down properly, even if it had. This was only when it was switched off at the wall, not after a restart or when the PC was left plugged in and switched on. She only uses the PC to look at You Tube and some webcams from her grandkids, and that's it, she's not very computer literate. Initially, I left Windows repair to run overnight, but when I looked at it the following morning it was still in the repair screen, so I assume it had hung. I spoke to a local repair shop and they suggested I test the RAM, test the hard drive, and replace the CMOS battery. The RAM and hard drive checks went without any errors and after I replaced the battery the hanging stopped. I played with the computer all evening and shut it down as normal and switched it off at the wall. Next day I thought I would start it up just to check it and I was faced with a "cmos checksum error - defaults loaded" message. I thought that was strange, but maybe the battery was dead, so I swapped it over with one from my perfectly working desktop to try it out, and my desktop worked fine, but after shutting down my mum's one it had the same problem when power was pulled. So, battery was ruled out. Incidentally, I will say that I reset the BIOS date and time every time I was faced with the error, following up with a save and exit. It worked fine until I unplugged the computer. I then moved on to the BIOS and set it back to default, and the same again. After this opened the case and used the jumpers to reset the BIOS to default again, but no difference. My mum will not leave it switched on at the wall constantly in case it self-combusts (same with her washing machine, TV, lamps,etc), otherwise I would just do that and ignore it. Is there anything else someone can suggest that I try? System: Shop bought by Mesh Motherboard is an ASUS PSN-E SLI 4gb Ram - samsung 128gb hard drive - ASUS Thanks for any help.