Acer Extensa Overheating Problem?

Ever since I bought this laptop I've had an issue of it shutting itself down. Almost always while watching youtube videos. I found out about the handy little tool called coretemp and I see my processors running about 68+ nearly all the time. When I have websites loaded that have flash animations, ads, videos (youtube), it only gets hotter and hotter. It nearly always reaches 90+ (Celsius) and then shuts down.

I read about it needing a bios update for many people who say they have the problem with the laptop screen going black, but I think mine is heat related.

My laptop runs around 68 when idle and when busy it gets hot. Right now I have Google Chrome open with two tabs, one is this webpage and the other is gmail and its running at 75 celsius. Performance tab in task manager says it has a processor load of only 1%.

I keep a watch on the temperature and as long as I start closing programs and windows when it reaches around 80 it will start to cool down. So as long as I can keep an eye on it the laptop will run fine for days with no problems. If I forget to check and it gets too hot it'll shut down. I'll check the logs and sure enough the last few lines of the last log file will look something like this

Time|Core 0 Temp|Core 1 Temp|Low Temp|High Temp|Load

4:06:57100°99°53°100°79%
4:07:0798°99°53°102°85%

Anyone else have this issue?

Edit: And it's on a hard surface so it's getting plenty of ventilation

yeah the fans are blowing air out. Quite warm air. It's the Acer Extensa 5420 (sorry thought I mentioned that). I dont have any pets but I probably do need to open it up and investigate more... I hate opening laptops though.

It's not very old. I think I got it in early 2008 and it started doing this probably witin a month after a i bought it. I just lived with it but its been getting worse.