Please help this is doing my head in can anyone remember a movie think it will have been early 90s about a guy who finds a pendant thing that comes from space and when he presses it he turns into a mutant I think it had something to to with a Geiger suit please help

It could be Laserblast (http://www.imdb.com/title/tt0077834/) from 1978.

There was a Marvel comic that came out around that time with a similar premise called Darkhawk.