Dell Inspiron 12 yrs old start and run problem

My Dell "Inspiron" desktop computer with Intel I-5 processer, and WIndows10 has developed a problem.  When I push the power button to start it up, The button goes into a sequence of a yellow blink, a white blink and then off for a couple seconds, and this keep repeating.  When the white blink comes on, the hard drive light very briefly blinks on.  The computer does not boot up.  Note it is supposed to go to a solid yellow  when it is put into or times into a sleep mode, and tstays solid white while operating normally.  I got it to work right once out of about 20 tries, and made sure I had everything I needed backed up to an external hard drive.  Pushing the button again while blinking does nothing (pushing it is supposed to also be a reset function).  The only way I can get it to stop blinking and be fully off is to unplug the power cord.  Before this started, once when I had let the computer go into a sleep mode,  When I hit a key to revive it,  the display came up but the display had colums of rectangular lines over the correct screen and everything was jittering up and down.  It also went to that mode once last week just sitting, fully booted up.

I'm wondering if this is a BIOS problem? a Hard Drive problem?  Is the blinking sequence some kind of error code that's trying to tell me something?

The thing is 12 years old and has been used almost every day, so  it may be dead.   It's not worth me taking it to a shop.  I'm not afraid to go into it to try and fix it if there is something I can look at.  I am a retired Electrical Engineer circuit designer, and many years ago worked for a couple years as an audio/stereo equipment repair tech, so I'm not afraid to take it apart.

Is the very brief blink of the hard drive light telling me the hard drive is not booting up and may be defective?

Interesting that it worked once after about 5 tries, but has not worked since - maybe an intermittent connector to the hard drive or something else?

Any thoughts?     A quick 2nd question - can I take out the CD_ROM drive and put it into a new WIndows11 computer if I buy one?  Most computers don't come with those any  more.

Thx,

Dave