My laptops 4520 is getting off suddenly.

What happens before is turns off? Do you receive any kind of errors? something happens?

It could be resulted by lose of power, let's say a dying battery, or maybe because the laptop is too warm.

Also, I would consider looking for viruses. There are viruses which can turn off the computer, but usually you see a count before turning off. Also could be hardware conflicting.

I would try the following- start the computer at safe mode, which can be done by pressing on F8 or F12 at restart. See what happens- if the computer turns off after a while, it's a power issue, and then you can try testing the battery and warmth of the laptop. If nothing happens and the computer looks fine, I would check if any recent installed hardware or software may have conflicted with something. Good luck and let me know