Booting in Safe Mode / Disk Defragment

Sys=XPpro-sp2.
PC will not boot in safe mode, gets to, sys32/drivers/agp440.sts and hangs up the box.

Tried to repaire the drive c/properties/tools/repair select “automaticly fix file system errors and dialog box says “chkdsk utility needs exclusive access and files can be accessed through restart” Reboot and chkdsk runs and I get the same results.

Error 2, “Disk Defragmenter has detected that Chkdsk is scheduled to run on the volumn: (C:). Please run Chkdsk /f.

How can I forse XP to boot in safe mode through dos?

Any sugestions on how to repair the disk?

Thank you in advance.
Sam