Laptop shutting down without warning (overheating?)

So it's weird I can usually run a few hours without it happening but it always happens at least two times a day and I know it's not normal I only brought the laptop at the end of July!! I make sure not to block the vents and fan but it still happens, any way to stop this from happening?

Laptop info:

Model: Acer Aspire 5733

Processor: Intrl Core i3 CPU M 380 @ 2.53GHz 2.53GHz

Running: Windows 7 Home Premium

I ran Speedfan 4.47 to see how hot my CPUs were and this is what I got:

HD0: 36C

Core 0: 40-45C

Core 1: 46C (average)

CPU usage was only around 4-7%

Already tried a can of compressed air on both side vent and fan and still happens.

Any help would be very helpful and it would be understandable if I hadn't just brought in at the end of July! Also it happens around every 20 minutes if I have it on my lap it gets really really hot when I have it on my bed or my lap and this is without blocking the fans.

Thanks in advance let me know if you need any more info.

EDIT: Just left the laptop on the desk just surfing the internet for an hour or so and Core 0 and Core 1 are at 70C+!!