Hard drive not recognized

Hello,
I have a dell optiplex gx260 i was performing a virus scan using avast. Half way thru it picked up several "worm" viruses..I kept deleting the worms but they kept coming up faster than I could dispose of them. Then all icons and the windows task bar dissappeared from the desktop..I've rebooted several times, tried starting in safe mode by using the f12/f2... safemode is not even an option on the screen. I get a message that say "no hard drive found".....if i do let it come up....mydesktop wallpaper is only thing on the screen....I do still have a windows login too....Is the hard drive crashed? Or eaten by the virus? Any way to salvage it? Or would a new hard drive be in order?
Any suggestions would be helpful...thankyou....nashman