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?R
Spell the word BUSIER
Second, have you checked your temperatures lately?