I've had a PC for around 2 yrs and my copy of XP Pro appears not to be genuine. I had the PC made for me and assumed that I'd get a genuine copy.
I dont want to store up problems for the future and would like to be "legit" so whats the easiest and cheapest solution. An OEM copy for less than £80 on line? Would this mean I would lose everything on my pc if I install the new legitimate version?
If you do have a pirate copy, just buying an OEM version and changing the product key may not work. many pirate versions are corporate copies, with different serial number sets than OEM, and retail version. Windows does know which set of serial numbers applies to which major XP types, and will reject ones which don't fit the correct range of numbers.
So the advice to get an OEM version, and do a clean install is by far the safest and most likely to work without causing you ongoing problems.
Unless you can persuade MS to supply you a legit copy in exchange, presumably, for some info about your pirated copy.