Need To Keep Reinstalling

I built a new PC a few months ago. It is running 32bit XP Pro, I have a RAID 0 which my OS and Programs are on, a RAID 1 that my files/data are kept on, and a backup HD that I just keep whacking backups over to. The problem started a few weeks ago, when Adobe Acrobat started having weird launch problems, to the point where I ended up deleting it, as the only part of Creative Suite CS4 that I don't really use as of now. I can't 100% remember the error, as figured I'd come back to it at a later date.

Next thing to happen, a week or so later, was that iTunes stops working after every turn off / turn on, or restart. i.e. iTunes is set up, all updated and working fine, until I turn my computer off. When I turn it back on again it hunts for some setup file, then says it can't find it, and refuses to open. I have to delete iTunes via Add/Remove, then install it again. At this point, on first opening it, all my music and settings are there fine, but once it's been turned off again same problem. This is a real pain in the *** even more so than usual as I have an iPhone now, so backing up is taking a while each week.Finally (I think), Office is doing a similar thing - it has been installed since first building the PC and working fine, but now each time I open any Office program after a restart it goes through some stage of installation again, and asks me to to activate it over the internet, yet again.

I don't think I've installed any new programs, bar program updates, and it just suddenly happened over a couple of weeks. It was working fine for a few months beforehand.I am relatively PC aware, but a long long way from expert, so have no idea where this problem is coming from - which has made Googling it impossible! It's like it forgets all its setup info at startup or shutdown, and has to start over again. NB, my AVG anti-virus is up to date and running Malware Bytes shows a clean system. Oh, that reminds me, I also had to turn off XP monitoring of my anti-virus, as around the same point as all this started XP started telling me it wasn't turned on or up to date, but it was running perfectly.