Show hidden files?

Hi,
first post of mine here.
Brief profile:
Very Very technically experienced, can fix any fault without re-install.
But...
My question:
For some reason I can no longer see hidden and system files. After selecting "show hidden..." it automatically (instantly) reverts back to default (don't show..) How do I fix this ?
I have tried:
Regfix (multiple programs)
Windows fixes (too many programs to mention)
Full Antivirus/spyware removal (multiple multiple progs)
This must be a registry error of some sort (I think it may be one of those tweek programs I installed,(which can all be reverted manually) I don't know when, as I wasn't checking hidden stuff)
It's very strange (nothing un-common here) I'm starting to think it's hardware. Except fresh install on another hdd works ok!
I have 140 Gig of data, and therefore presently don't want to format just due to this ONE and only error
Kim

 

Thank-you
mine was set to registry entry 3 (which wasn't one of the options)
All ok now.
Kim