My system boot up time is very low ,,, how...

when you power up computer press F8 key then enter in safe mode.
Then type following coomand in run
%tmp%
prefetch
remove all files .
then type in run "chkdsk /r"
then presss "y"
then when u restart it fix error on harddisk.
Aslo check there is not 2 antivirus in system .
scan your computer with updated antivirus.

I would back up your files into a external hard drive, then use the recovery cd's that came with the machine or a windows installation cd to reinstall windows to the computer.

Since you are starting fresh this way, your computer performance will be like it was when it was new.

After the windows setup if you used the windows installation cd, you will need to download the drivers for your machine from its makers website to get all functions of the computer to work properly.

go to safe mode, press F8 before the system up.. at the windows safe mode, type in the RUN command MSCONFIG and select STARTUP then DISABLE ALL, then restart the PC...