Sorry about the vague title but I am running out of ideas to fix problems with a computer. The pc in question is a shuttle xpc that originally had a less that legal copy of Windows XP pro on it. I was asked to provide a legal copy of windows XP and reload all of the software, which I have done numerous times. The shuttle had a new mobo installed about 12 months ago. Originally I installed XP and was experiencing all sorts of minor niggles with it, so I ran some diagnostics which revealed some faulty memory which I replaced with some good memory (Crucial) I have reloaded Xp about a week ago but was having lots of minor problems with it, update not working, IE7 crashing etc. I ran checks on the memory and hard drive but again both came up OK. I have just repartitioned and formatted the hard drive and reloaded XP yet again, which loaded without a problem, and am back where I started. I went to install AVG but it told me the downloaded file was corrupt, I tried to install it from my memory stick but again the same problem. This time the updates downloaded and installed OK but whenever I open IE7 it throws up an error message saying it needs to close, problem with mshtml.dll. I tried to open My Computer and it says there is a problem with explorer and needs to close. The problem suggests to me a data corruption issue but checks on the obvious culprits (memory and hard drive) don't suggest a problem, whether its another motherboard problem I don't know. I did wonder if it could be a faulty CD but as its a new one it should be Ok. Apologies for the ramblings but I am tearing out what little hair I have left, has anyone any suggestions as to what the heck is going on here?