Fan, Overheating problems, computer shuts down

I have an aspire one netbook...zg5 model. I have been having fan/overheating problems, and have one time already removed and cleaned the fan, and installed the addon for fan control. That worked for perhaps one year, and then fan seemed to slow unit down to a crawl, when it went on full blast. So, I installed a new fan. Now the unit cuts off after turning it on, after 1 minute or so. The only thing that worked, to keep the computer on, was putting it in the freezer, not much of a solution. It sounds like the fan is turning, but I can't keep the unit on. It cut off when it hit 50 c. I am wondering if it is the thermal paste, or perhaps something else involving the motherboard, or heat damage to the unit. Any ideas??