Blinking Error Codes 3 Long 5 Short CPU Not Detected

[rbrennan]

After 2 weeks turned off, my HP Pavilion x360 crashed and then never recovered.  After a hard boot, I was presented with blinking error code: 3 long 5 short CPU.  After going to the end of the internet it seem the error is CPU Not Detected.

The history:

This computer was a hand-me-down from my mother as she used it for about a month, decided she didn't like it and put back in the box and put it under the bed...because that is what old people do.  It was in 'storage' for a year, maybe 2.  She then remembered that it was there and gave it to me.  After about 3 months, it crashed with blinking error codes (it was a while ago and I can't remember exactly the sequence of codes other than it was not pleasant codes).  Dr. Google suggested many things and I tired many of those things, but to no-avail, I took the plunge and replaced the motherboard.  NOW 6-8 months after I replaced the motherboard, it has happened again.

I found that many folks have had the same problem with 3.5 blinking, but I can't seem to find the solution.  Links to the suggested solution are broken as this is likely a very old issue.

Please advise.