My screen is flickering :(! Help!

Alright so, as you can see in the photo that is how it looks like.

My Mac is from Mid 2010 21.5” with 4 GB RAM, running on High Sierra. I have tried searching for a solution online, but I can’t find anyone, who had the same problem as mine.

What I’ve tried so far:

• Reboot and redownload everything. (Deleted the whole Mac), and still the flickering is happening and keeps shows up.
• I’ve tried reset NVRAM and SMC, still did not work.
• Start up on recovery Mode, still did not work. (Also I pressed down D).
• Updated newest software.

Symptoms other then the flickering screen:

• I woke up this morning, and the flickering was gone for like 20 mins, and came back.
• The computer is heating up a lot.
• The computer ONLY STARTS UP if I hold the down shift key! If i start up normally, then it freezes halfway through booting/loading. (or opening or whatever you call it)

This confuses me, and I hope someone can help.