Q: Is RAM my issue??

Hiya i'm having some problems - hoping for advice as have no clue . Just upgraded to yosemite & garageband 10.3 but now keeps bringing up system overload  10011 or that its too slow - i  used memory clean which helped for a while but now even if it says i got 1.50gb (out of my 4gb) free it still stops during playback.

I am a bit tight on cash & desperate to get on with my music so want to make the right decision. Do u think upgrading to 8gb will solve my issue or is there other things i can try or diagnostics i can run? is it maybe something to do with yosemite?

i've cleared over 100gb Hardrive space and i checked CPU activity which at max peak was 55%.

During my session just now my entire system just shut down & then restarted....which seems worrying!!

Any advice would be greatly appreciated.

Drea