unremovable viruses and unrepairable errors

I have bought original Kaspersky internet protection 2009 and after scanning it shows no viruses anymore. but my pc is not working normall as many of the folders are forcibly hidden and the folder options aint helping to uncheck the 'do not show hidden files' option. in starting the OS 1st thing after booting there comes an error called 'qhonsvc'.exe. Comp volume slows down automatically. and many more problems. the service guy recommends to format the hard disk and reload the OS which i think is the easy way out to solve the trouble. but i am not able to backup the folders and files as they are hidden somewhere and are difficult to retrieve.
PLEASE HELP!!!!!!!

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