Question REALLY weird error/screen shown before boot (also newbie alert)

Jun 26, 2019
okay sorry if i have posted this in the wrong section, i dont really know where to post this.
Also i am asking this because of my curiosity.
I had a compaq with pentium 4 (model somewhat like compaq sr2170nx ). The thing is that whenever i used to boot it up, no POST, no Beep, and it used to give a screen of -'grey,pink and green with glitched letters, some letters were blinking' in a second or two.
i had some important info in that computer so i used a kaspersky rescue disk, and it would directly boot up with the disk, i noted down my required documents. And i again tried to boot it up 4-5 times without the disk but failed.
I thought that he is now dead. But booted it after around 1 month, and now it booted up normally without any data loss, etc.
I just want to know what was it because i never found on google what was it.
Thanks, (and sorry for bad english)