Black screen before login, can't find cause

[od33]

I'd really appreciate some help - for some reason my setup now won't get to the login screen, I get the green progress bar and (c) Microsoft, but no windows logo, then a black screen. When I've tried to repair windows I get a message saying startup repair cannot repair this computer, with the problem details showing:
Problem event name: startuprepairoffline
Signature 1: 0.0.0.0
2: 6.1.7.7600.16385
3: unknown
4: 21200435
5: autofailover
6: 8
7: norootcause
Os version: 6.1.7600.2.0.0.256.1
Locale id: 1033

I've run chkdsk, system file checker (both came back clean) and I think I repaired my MBR (I can't remember as I've tried so many things). I've also run boot logging but don't really know how to interpret the resuts, the last entry is "Loaded driver \SystemRoot\system32\DRIVERS\vwifimp.sys", the last successfully loaded driver is "\SystemRoot\system32\DRIVERS\AVGIDSEH.Sys". I renamed my AVG entries in case they were causing the problem but it didn't help. I also disabled my graphics card in safe mode and rebooted which did then allow me to log in normally, however the next time I booted it went back to the black screen.

At some point I do remember seeing a message saying the problem was due to system configuration changes - I haven't changed the configuration but the only thing I can think is that my graphics card came out of its slot while the PC was on the other day, it worked fine after but that's the only thing I can think of that might have caused a problem. All I'm able to do now is log in to safe mode - can anyone help? I've resigned myself to reinstalling windows (which will be a complete nightmare) but I'm worried the problem might reoccur even if I do this. Any help much appreciated, I'm totally stuck.

My system is an i7 2600k, Asus P8P67, 16gig ram, 1x Samsung system SSD and two other HDD, AMD R9 270 GPU.

 

[vrumor]

GPUs just dont come out of their slots if they are properly installed. Did you drop the PC?

 

[od33]

I moved the PC to access the rear ports, the graphics card was came out of its slot due to the monitor cable pulling on it. It is still functioning in safe mode and when I managed to log in normally on the one occasion since this started so I don't know it it's related or not.

 

[vrumor]

If something is removed from its slot, the GPU in this case, while the PC is on, is about the worst thing you can do to a PC short of submerging it in water. If this started to happen right after the GPU was pulled out while powered on, common sense would dictate that is a good place to start to solve your issue.

 

[od33]

Thanks, however my problem didn't start right after the incident with the gpu, there were several days where it continued to work normally, which is why I'm unsure as to whether it is related. Also windows will boot in safe mode, but won't boot normally even when I disable the gpu driver and try to run with generic graphics drivers. I'm just trying to see if anyone with more expertise than me can work out from the boot log or my description what might be causing the problem.