HELP Please xp

[klo]

Hi.

I'm running xp proffesional at home, I was deleting some files, from which I had installed a program, this included the one out of the system registry. I turned off my computer after doing all this like it told me to, and restarted it. Now first thing I noticed on the start up screen is that it was only reading 200 and something ram, and I know that it has 360 ram. Then it went into the menu options on how you would like to start my computer (safe mode ect) it will not allow me to select any of the options and won't start itself, it goes to a black screen and at this point I notice the hard drive (drives) arent' reading. I cannot do a setup either as it keeps asking for a password, now I put this together myself and never recall putting a password on there.
Any thought's on how to solve this would be greatly appreciated.

Thanks
Kirsty