Windows 7 PC Won't Boot - Stops At ClassPNP.sys

I've ended up with a PC that refuses to boot - gets as far as the "Starting Windows" screen, waits for a while and reboots - repeatedly.

Starting in Safe Mode, it gets as far as ClassPNP.sys before stopping (for some time) and rebooting.

I've tried:

• Startup Repair - fails with an error that what looks like (and what I can remember), "O/S does not match".
• I do not possess the installation DVD.
• The BIOS does not have the option to switch between IDE, ACHI, Auto, etc. The BIOS has been 'factory reset'.
• I've run CHKDSK more than once, with auto-repair (and some other option, can't remember which).
• I've run SFC with the (what I can remember as) the C:\ and C:\Windows specified, several times, each time it ends with "I've tried to fix it, but I can't". So I got the CBS.Log onto another machine, ran the command that extracts the "SR" entries into another file. When I examined that file, all of the entries looked "OK" (no errors). All of the errors I could find were to do with Windows Updates (and 'TrustedInstaller' giving up).
• "SeaTools" does not report the drive as defective.

I've attached the CBS.Log, here.

What else can I check? Can anyone help, please?

Thanks for the replies, but neither SeaTools (Seagate Drive Tool) or CrystalDiskMark report the drive as defective (certainly no more defective than the machine I am typing this on).

AddRAM said:

Create a system repair disc or install DVD (from another PC) and try a System Restore from boot.

I managed to find and build a bootable Win7 ISO on a USB stick - it would only perform a 'Clean Install', not a 'Repair Install'. There are no backups of this machine (it's not mine). The repair options gave me the same messages as before.