I use to work on these laptops back in the day. To clean the fan out you can't access it from the bottom. You could just blow air into the vent on the side with an air compressor. You could remove two (i think) screws from the bottom case (near the back) that hold in the keyboard cover. Pop the keyboard cover off (e.g keyboard cover is the thing that has all the media buttons including the power button), and remove the keyboard.
You should see a heatsink and fan like this one
You can blow that out and it might fix your issue. There is another issue that these laptops have that cause over heating. Notice the 4 screw holes in the heat sink. There are 4 screws with springs that hold that heat sink down on the processor. The screw stand offs are known to break off the board so the heat sink is not held down firmly on the processor. This can be fixed, but your going to need a soldering iron and solder. You can test to see if it has this issue by gently lifting up on the heatsink to see if its held down firmly.
To fix this issue: remove the heatsink and remove the stand offs from the screws (the ones that broke off the board (you might need pilers for this). Simply put the screw stand off back on teh board, turn your soldering iron on high and press it down with the soldering iron until it gets hot enough to remelt the solder on the board. Apply new solder does it doesn't happen again. Thats it.. very easy fix. I use to do this to every p900 unit I ran across to prevent reworks.
This is a ****** image, but you see the 4 holes around the processor? Thats where the screw stand offs should be soldered to. Kinda funny i found this pic on a website that sells system boards and its missing the stand offs.. classic.