I'm having an odd issue

I've been working on a project for a couple of months (with only the normal maya problems).

and then today after working and rendering all morning, I hit render:
using mental ray I only got a black screen.
tried maya software and also got a black screen.
Tried maya vector and got a black screen.
tried maya hardware and it rendered.

worse now I can''t even render a simple ball over a surface with one light.
Just comes out back...

All the previously fine files I've tried will not render (unless is maya hardware mode)

I tried resetting to defaults
I tried repairing maya using the install menu.
I tried uninstalling reinstalling.

Nothing is working.

If i show materials all the shaders look fine in the modeling panels.
UV's are fine
shaders are all connected.

Could my lights have spontaneously become disconnected from the render engine?

I've opened this file up on a different computer and am having similar issues - but it hasn't broken everything - scared me at first until I tried another file and Mental ray rendered it fine.


I'm in the process of uninstalling and regedit-ing every and any registry mention of maya out of my computer and will try another reinstall.


Any Ideas?

I'm at a loss

Thanks...

Win 7, i7-930, geforce 9800 GTX+ Maya 2011