I also have a lap top ,samsung R 510 that keeps on freezing after working for about five mins, can not even sign out . I have to remove battery and re-start computer ,and then it freezes again .HELP.
I feel sure that VHG is on the right track and has given you good advice; especially about avoiding using a laptop on soft surfaces.... which would include one's lap.
My only doubt is cleaning vents with a hair drier which I feel could blow dust into the computer......Perhaps what I have is required.( A mini Vac.) :-