c: not found on hard disk

I have acer aspire 4930, running on windows xp. the os was working fine, in order to shut it down my brother pressed the power button and hold to forse shutdown it.
when i started the system today, it was way too slow. it somehow managed to show me the desktop but still was not able to even open task manager. a few minutes later my antivirus showed error. C: not found on computer please follow the steps and steps were to set c: from disk management.

I don't know what to do, tried system restore, but it took 25 minutes to show the restore point and even after selection of restore point a popup came, "restore cannot reflect changes done to c:". please help,

 

http://support.microsoft.com/kb/315265/en-us
How to perform checkdisk

if you do not have Recovery Console installed, then run from the start menu

go to start, run, type in cmd

in cmd type in chkdsk c: /r and press enter

type Y for yes and press enter

type exit and press enter

restart pc, allow checkdisk to finish and run again until no errors are found


this is a lengthy process depending on the size of your harddrive, the percentages will fluctuate, this is normal, you can view report in the event viewer.
go to start>run> and type in eventvwr.msc, click on the applications directory, and in the right hand panel choose winlogon.

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