Try getting it to the point when you have teh option of start-up repair, (usually if you suddenly disconnect the power)
From there you can have the option to restore the pc, it will ask you whether you want to restore froma restore point, and further down say advanced options, here you can revert back to factory settings.
My laptop had that issue back in 2011, thats how i fixed it, though im not 100% sure if the system restore can be accessed like that, just a guess.
If nothing works, either buy a new copy of w7 and install that or get one from somewhere like tpb.
This is most likely a hdd problem as that was what it was for me or it would allow you to boot to safe mode as the core drivers for safe mode should just load if you never changed them.
What drivers where you updating?