My old HP pentium 3 vectra pc got messed up when I was trying to re-install (repair) XP professional after getting warnings that some of the files were replaced by unrecognisable versions. I had bought the PC second hand and without its original install HP disc so I used a different XP professional disc that I owned, obviously with a different serial number from the original one. After an unsuccessful reinstall (which hung up), when I restarted the PC it halted to a dark screen after the POST screen in which it correctly recognised the memory and details of hard drive. Now if I use HP recovery disc meant for my 2nd more modern PC, it correctly detects that there is an operating system on the drive but obviously states that it is not meant for that installed version. I have tried to boot from the with XP disc in my CD Rom after making boot from CD my 1st priority in the BIOS but 1- Neither does that kick start the existing XP 2-Nor does a fresh installation of XP start; simply a black screen stares at me! I have tried all options in the order of priority of devices to boot from ,but no effect. F2, F6,F8 dont work. Could microsoft/HP have a role in preventing re-install from a different disc than originally on the hard drive? What may I do 1-to reboot into this hard drive 2- Or at least to re-freshen the system files so that i do not loose the existing staff on drive by a total format 3-If none of the above options is viable then how to format and do a new clean install now that the pc gives no responce to the presence of XP cd in the CD Rom drive? 4-If I remove a hard drive with system pre-installed on it from another PC and stick it into this PC then is that likely to work or will there be a conflict of it with different motherboard or will XP refuse to work that it was not installed for this different hardware combination; if yes then what is the way out for that scenario? Sorry I haven't had this PC for long to have made a back up or restore disc! Silly me Please use fewer technical terms and abbreviations in Ur advice and I will have little problem in following it. Many thanks to you all trying to for help!