Computer issues after deleting cache files

Hi - I am having issues with the following computer:

iMac 21.5 inch Late 2012 running on Mojave v. 10.14.4

Processor: 2.7 Ghz Intel Core i5

Memory: 8 GB 1600 mhz DDR3

HD: SATA Disk 1 TB

Peripherals:

Apple External dvd player

Seagate backup plus portable drive 3 TB ( for time machine)

The computer had been sluggish for a couple of years so a few months ago I read up that you could speed up your computer by deleting the cache files so I followed this Youtube video: https://www.youtube.com/watch?v=bXCAmYxdzcI

I deleted the following cache files:

~/Library/Caches

Macintosh HD/Library/Caches

Macintosh HD/System/Library/Caches

This did speed up my computer at first but then it began behaving erratically.

It now does the following:

When waking from sleep after a few hours it goes to a grey screen, with a status bar running at the bottom. It goes to blue screen after three minutes but it takes another couple of minutes for the wireless mouse and keyboard to work. This does not happen however when I have the time machine external HD plugged into the computer.

The computer also has frequent freezing bouts. The spinning wheel shows up while using Safari, or Apple Mail, or other programs. It can stay like this for up to a minute. When typing an email the letters actually freeze at times.

After having these issues I was going to restore what I had deleted through Time Machine but couldn't find these files there.

Since then I have done the following to try to get this computer back to normal but without success:

Got anti virus software (Total AV) - did a complete system scan - got rid of all viruses

Reset PRAM

Reinstalled MAC OS

Reset computer to factory settings - it went back to Tiger. Then did a full system restore from Time Machine

I thought I had solved the problem with the last solution but the computer started freezing again after a few days of use.

This makes me wonder if I have a hardware issue or if there is something corrupt with the time machine backup.

Any advice/help would be greatly appreciated

Thank you