Lost admin account, Vista

[display]

I had two accounts running on my PC, the admin and the guest account.
I updated to SP1, two days later the admin account is not visable anymore...guest account still works as it should (no admin privilege). Any thoughts on how to restore the admin account?

display

Update 2008-04-23
Trying start start in fail safe mode - doesn't work:'(
The instruction is to press - start/lock/restart - when pressing "lock" the login page comes up and I can see that the guest account is locked, but there is no "restart" button...what am I supposed do? Hit the reset button on the chassi?

I've also tried to find a way to check my harddisk...but in the guest account I got no privileges...is there anyway to log on as admin while in guest account...so that I can use the system tools?

Just realised that I missed saying hello to everyone on this forum, so here it comes... Hi All ;-)

display

[display]

but there is no "restart" button...what am I supposed do? Hit the reset button on the chassi?

Update 2008-04-23...later
Done some trial & error...
By hitting the Lock key and then doing a hard reset (reset button) I finally could boot in failsafe mode and log in as admin, my files/dokuments were intact...phuuh...
Moved them an other HD...and re-installing Vista (clean)...and then a month to get all programs/drivers/etc up to speed...well it could have been worse.

Conclusion...Vista SP1 - Backup, before install it !!!