For the last week or so my FSX has been hanging after a few minutes of flight. I can still hear the engines and see what was on the screen when it froze but nothing is moving and the only thing I can do is CTRL-Alt-Del and shut down. Please help. I have cleaned registry and defragmented.

If it's anything like mine, and I hate to be the bearer of bad tidings, then your hard drive is about to have an epic fail!

One thing I didn't do though, even though I suspected HD problems, was do a complete and full backup at the first sign of trouble.   Lost a lot of pics and music.

also try deleteing your FSX.CFG (not found in your Microsoft Games / FSX folder, but burried deep in your computer in hidden files.)  Delete the FSX.CFG {or at least just move it to your desktop so FSX has to rebuild a new one...} and after it builds a new one, see if the problem still exists. 

If it does, and your Heat Sink and fan are all in working order, start looking around for a new harddrive and start backing up your Pictures and Music before you wish you had more time.

it is probably your graphics card then,i have the same problem and i know mine is rubbish.

Honest truth, (though strangely as of yet unmentioned) this kind of problem, with any software, can be the result of file corruption from a bad add on, an error while the game was running, or a conflict with new hardware. try reinstalling FSX. also, there are both reports of extreme heating on the 280.26 drivers, unrelated to FSX, and also, conversely, errors with FSX, even when overheating isn't the problem. roll back your drivers, and see what happens.

Here's something else. I also logged on to my computer as another user and had the same problem. I believe this would involve a different FSX.cfg file, so that is probably an indication it's not that file causing the problem.

I tried to find FSX.cfg when you mentioned it befoe but I could not find it.

Thanks, I will let you know how it turns out after Labor Day.

Ground Hog, I also have the same issues you're having and I've determined that unfortunately there is no answer to this issue; memory, overheating, drivers, cfg files, this and that  could be an issue, either separately or in conjungtion, but I do not believe so (I'm no computer expert by any means), chances are the issue is with running FSX under Windows 7, this is a new platform, Windows from its inceptcion has always had issues and they still persist and even different ones are piling up over the older ones . This problem is so intermitent that it is almost impossible to diagnose, let us not forget that we are not running FSX as it comes from the disk, we've added tons of addons, such as aircraft, scenerys, textures, missions, etc. etc.
I've read as much as possible about this issue and haven't found the correct fix yet, sadly. Just to give you an idea, sometimes during my flight session, which last for about an hour I don't have any freezes at all, sometimes only one, yesterday I had 3, go figure, I'm usually also running Plan G, they both freeze at the same time, but it sometimes freezes up even when Plan G is not running, also, I have full control of Windows, I can surf the net and do whatever I want, while FSX and PlanG are Not Responding, at first the only way out was to shut them both down through Task Manager, but if left alone, they'll start running in about 6 to 10 minutes as if nothing had happened and I'm able to fly the entire session without any problems, except yesterday, where I had 3 freezes (I was also flying a new airplane, new install), perhaps this had something to do with it.
I'm going to try next to fly stock airplanes in stock scenerys and see what happens, perhaps it is our weather in Tampabay that doesn't help. By the way, my rig is only about 6 months old and runs like a champ, 4 cores at 3.5 GHZ running without any changes, all temps are in the cool zone, I also fly Rise of Flight and Over Flanders Fields with no problems at all, so this issue  has nothing to do with hardrive ready to go out or old drivers or whatever one might think of.
Man, I wish I had an answer, as I really enjoy this sim, more than any other one, if you find the answer to the problem, would you please shoot me a line, will do likewise.
Best wishes,

Nope, it didn't work, Yesterday had two freezes, go figure what makes this thing tick! Grrrrrrrrr.....!