First of all, when your system freezes, you don't need to press the power switch to turn it off.
You should use REISUB (safe reboot).
1. Hold down the Alt and SysRq (Print Screen) keys.
2. While holding those down, type the following keys in order, several seconds apart: REISUB
3. Computer should reboot.
How to remember?
Raising
Elephants
Is
So
Utterly
Boring
or
Reboot
Even
If
System
Utterly
Broken
or
Spell the word
BUSIER backwards

Second, have you checked your temperatures lately?