PC (VISTA) will not boot up ...

The PC will not boot up. Even in safe mode it goes to

windows\system32\drivers\crcdisk.sys

and hangs for a while. Then it goes to the screen asking whether to go to Safe Mode, Normal Startup etc. When I select Safe Mode (or Normal Startup), it goes through the same process and hangs on the same file. I think the thing to do is run

chkdsk /r and/or sfc /scannow

but I cannot get far enough to enter those commands. Please help!

Thanks ...