Overheating issue with xbox 360?

Alright just to clarify I have the original xbox 360 not the slim. Anyways I've tried just about everything fixing this darn thing, I've had it since 07 and about 2 years ago I got the ring of death. Microsoft fixed it for me and replaced the old clamps. A little over a year ago I was having problems with overheating issues again. I've tried cleaning all the dust out of it, I've checked the power that's coming through and everything seems fine. Then I took the clamps off and the compound was completely deteriated, it was hard as plastic so I removed it with rubbing alcohol took about an hour or so then I replaced the compound with the proper amount. Worked fine for about an hour then it started again. Since last week I can only play my games about 15 to 30 minutes before it either freezes or gives me a entirely blue screen. I have an external hard drive connected that I have movies on and watch and I can only watch 1 before it freezes again. Usually it'll freeze right after I exit to the dashboard with movies but games will freeze before I can get 15 minutes of play. Depending on the game. Before I get complains on pirating I just want to ensure all these movies are rips of my own dvds that I prefer watching on the hard drive because it lasts longer than when they run on disc. Any suggestions? Looking for professional answers only, no towel tricks or amateur fixes that actually ruin the xbox rather than fixing the problem.