My computer always dies.

Today is monday. Monday is new week beginning.
In this week I am not sure whether we will get the order. We are still free.
Last week my computer in my home didn't work. When I turn on, It begins buzzing.
Then I unsettled the computer. And cleaned it completely. I saw the cream on CPU dry. But I couldn't find a little. After cleaning,I mount them all.
The computer can work when I turn on the power. After an hour, the computer dies when I was killing virus. Then I use the keys "Alt+Ctrl+Del" to restart it. But it didn't work. I only pressed reset. It will restart again. Unfortunately, after a while the computer shut off again.
I am not sure whether it is because the problem of cream on the CPU and thermal moudle.
I hope there are some experts giving me some guiding.