Windows 7 broken: can no longer log in...

Hi there,

Sorry if this post is quite long, but it summarizes a whole day spent attempting to fix my broken system

Back to office this morning I found my Windows 7 SP1 (Ultimate x64) rebooted and entered in the "startup repair" procedure. Was really weird to me considering I left it yesterday at night powered on, and that it is configured to hibernate later on in the night, and to wake up at 8 am, just before I arrive to office.
Moreover, other machines let me say that there were no power outage.

After it attempted to repair, I rebooted and landed on the W7 Welcome screen, but with only one account, of which icon was empty (transparent), and no user name was proposed (to be fill in). So, I tried to key each of my accounts with associated PW, but all were denied access.

So, I spent the whole day to try multiple potential solutions found on the Net (including your forums), but I always ended up to the same issue: unable to log in. Here is what I've tried so far (not in exact chronological order):
- rebooted and tried "Last known good"
- rebooted with installation DVD, chosen "Repair":
* tried "startup repair"
* tried "system restore", took 10+ min. to restore the last Restore Point generated yesterday, but ended up with the same login issue
* tried "command prompt": let me see that all my 4 partitions are accessible with (apparently) all stuff in place
o chkdsk /b /r /v
o sfc /scannow /offbootdir:c:\ /offwindir:c:\windows, as per one of your tutorials, but was told that it could not start the repair service,
o sfc /scannow, but I'm always told that a system repair is pending and that I must reboot and try again...
o bootrec:
. /FixBoot: operation OK, but same issue anyway
. /FixMbr: operation OK, but same issue anyway
. /ScanOs: told me that it found 0 Windows installations
. /RebuildBCD: told me the same
o tried to rename currently present bcd & bcd.log*, as per another forum suggestion, and then rebooted
- rebooted in safe mode:
* but crashed with a BSOD just after displaying "Classupnp.sys"
* unfortunately my system is configured to restart after BSOD so I could not write down error number & other info,
* so, not knowing if "Classupnp.sys" was the driver currently loading or the last one properly loaded, I tried to replace it with the installation DVD one, but without success

I probably forgot some other attempts...

Anyway, I'm now out of idea, and my last resort is to reinstall W7, but I would like to avoid it, hence why I hope that you'll find a way to fix my current installation.
BTW, I'm puzzled by the fact my system rebooted, the only reason I can imagine is that it crashes with a BSOD, and that tried to reboot. So, the cause could be a new HW, but I didn't install one recently (just moved a USB bluetooth adapter from a USB slot to another), or the consequence of a system update (but sounds not very likely), or some malware.

Precision: FWIW I must tell that my OS is configured to have "Program Files" folders and user profiles on other drives that the system one thanks to junction points :
- C: is the system and boot drive, "\Users" is a junction to "F:\Users", while "Program Files" (and its x86 counterpart) is a junction to "E:\Program Files"
- D: is dedicated to the swap file
- E: holds installed applications
- F: user data
It's running like this for, years.

Thanks in advance for your help

Wait one

Trying to find another member to help. Give me a couple of more minutes. About to go to bed.

sfc /scannow /offbootdir:c:\ /offwindir:c:\windows, as per one of your tutorials, but was told that it could not start the repair service,
o sfc /scannow, but I'm always told that a system repair is pending and that I must reboot and try again...

did you do the sfc/scannow command from "repair disk", "installation dvd", or by pressing F8 and enter "repair computer"? Don't do it using F8 as most of the time sfc/scannow doesn't work then. Sure your prompt was X: instead of C: when doing the command? Do a DIR C:\ in "recovery environment" to be very sure C: is indeed windows partition