Computercrash

A week ago my mac crashed, flickering screens & double screens.
Trying to unpower and restart again.
After minutes the same flickering screen...
Then a beautiful green screen.
More double screens....frozen screens.
Nothing seemed to help, it went so bad that my computer started to restart and knock down again,
several times in a row so that would not be a very good thing as well.
I decided to bringr it away for some inspection.
Don't know how long it takes.