Recover My Files and Fix Registry...

I have windows vista installed on my machine, and before 2 weeks ago it was working super fine.However now there are lot of error messages coming and some programs like internet explorer stops working suddenly.

I think some of my files should have been deleted by my little sister.So is there any software to fix the registry issues and recover the deleted files at the same time. I also tried to re-install applications.But it is not working. It stops and gives error messages during the installation.

I can't format the PC cause i can't go in to boot menu. (Cause password is missing). I have heard about something called registry cleaners.but is there a software to do both optimizing the PC and recovering the files.

Oh, and give your sis her own login in future, with limited permissions

Sure, but all a cleaner does is remove old registry entries that are no longer in use. They are left over from removed applications and the like. A good virus / spyware scan should be a higher priority.

The error message has to do with your RAM and indicates that there is a problem with it.
It could be that the RAM isnt seated correctly, or theres some dust. Reseat your RAM and clean out the dust with some canned air.
If you are using more than one RAM stick then try booting with each individually and see if the error persists. If you can isolate the error to one stick then you got your culprit.
Other than that, grab MEMTEST and again use on each module individually.

Btw i forgot to say i think that resetting CMOS will reset your password for the boot menu. I say i think, because i havent encountered a boot menu password before. Be warned that will clear your BIOS though, so any configuration and overclocking will be lost. To clear your CMOS take out the circular battery on your motherboard for 30 secs (looks like a big watch battery!)