windows activation

I have a pentium 2 bought from a garage sell...it has (had)win xp pro on it.....I tried to instal a new video card...and after I installed it I got the message that there was a major change in the system hardware so I have to reactivate windows...now I am stucked...the system does not let me log in again...is there anything I can do to bring the system back to life?
thank you all
you have been always so fast and helpfull

 

can you even boot to windows? if so, you will need to call Microsoft and get a new activation number. they have been very helpful in my past experiences, although their english is sometimes hard to understand lol. If you can get your hands on a windows disk, reinstall it and then reactivate it.

 

yes..I think I am stucked...I do not have the original disk...yes..it boots on windows....what amazes me is how other installed this on such old computer and how it activated it? because I suppose the original disk was first installed on much newer machine....and since one machine ...one disk...you know what I mean....
thx

 

you're better off installing windows 98 or 2000. a pentium 2 with im guessing less than 256 ram cant run XP decently.