hi,
My dell vista computer is in complete turmoil.
First of all my computer's cmd.exe had started to crash as soon as i initiated it. So i had made a mistake of deleting it. AS soon as i logged in...it wud say..."U have made an unauthorised change to windows. Winodowsis not activated".I restored the system and it got ok. then i replaced the cmd.exe with a cmd.exe of an XP system. ( i have told this as i presume that this will provide a clue to my problem)

Now the system completely switches off(not turn off....all the lights also turn blank and d system has to b booted again) whenever my brother is using his account.

Now today when i booted my system, it gave the same error..."unauthorised change....". i chose to "Learn More". It opened firefox and the windows page which was supposed to check my windows genuinity. And to my suprise it did not pass the genuinity test. ( My copy of windows is genuine 100%).
SO i restored my system again using the repair disk, and have been able to boot.
I need a solution or otherwise i will have to format it..
thx in advance