Why is my Toshiba A105 turning off by itself?

My computer is truning itself off when I am away from it for awhile. This is something that has just started a couple of days ago. I leave it placed where I feel it should be getting adequate ventillation. I have not changed my habits at all with where I leave it it turned on. It has all of a sudden been getting warmer. I had no problem whatsoever with it getting warm until a few days ago. I have had this since the end of Dec 2006. I owned another brand that turned off when it got too hot. I wouldn't think that this is the problem since I keep the fan setting on the highest. I rarely run it off the battery. I pretty much keep it plugged in all the time since I am always right by an outlet. I do try to drain the battery about once a week. Any help would be greatly appreciated. Thanks!

An additional note I just had it turn itself off while i was in the middle of doing something. I had it plugged in. Also the computer was in my opinion just warm. My other notebook would get much much hotter before doing this.

Another thing I am concerned about and not sure if this could be a related issue is that for this to have 2gb of ram it runs awfully slow a good bit of the time. Don't know if this additional information will help anyone to be able to let me know what is goingon and how to fix this.

I am beginning to think I should have gone with the advice of not to buy a Toshiba.