After using 20 to 30 min my Hp G61 lap top goes in hibernate stage and switched off . while rebooting it again it gives me a message that the CPU tem has reached more 90 degree so it got switched off . enter to resume system , please help me on this.
When you're using the laptop, are all the vents unobstructed. Most laptops pull air in from the bottom and blow the hot air out the back. Are you using your laptop on your bed or pillow or something that will stop air from being drawn in the bottom. If the answer is yes, the the fix is easy, stop using it on your bed.
If the answer is no, it gets more complicated. It is likely your heatsink is full of dust. The best way to clean it is to disassemble it far enough to expose the heatsink. Then used compressed air to blow the dust out of it. When doing this, you'll want to keep the fan from spinning. If you let the blast of air spin the fan, it may get it going so fast that it damages the fan bearing.
The less effective way if you are reluctant to disassemble your laptop is to direct short blasts of air in from the bottom and back where the air is drawn in / blown out. You should see the dust coming out. You need to use short blasts of air with like 10 seconds between blasts to give the fan time to stop spinning so that you don't get it spinning too fast. The other down side to this method is that some of the dust may be pushed out onto the motherboard inside the case.