Hi!
One beep then three beeps with a blinking red light, is probably APU issues...
You need to reflow or reball it.
Reflow and reballing are actual 2 different things.
Reflow: Melting the solder under the APU and let is harden again. This will solve solder cracks/colt joints. Most of the time it's a temporary fix... Not sure for how long, that depends.
Reball: Removing the APU and do all the solder work over again with good quality solder. As well for the APU as for the motherboard. Then put the APU (good positioned offcourse) back on the motherboard. This should be the fix you want. But it's way more difficult.
At this moment those 2 options are your only options to fix the APU at the moment.
Good luck with the repair and let us know how it goes!