Inspiron boots...sometimes

Hi!

I have an issue with my Dell Inspiron 15 3521. It mostly beeps on startup and doesnt pass a POST. However, every couple of times it boots and OS is loading... And it works until next power off / restart. I can also suspend and resume without problems.

About beeping - it beeps once so I guess it may be a motherboard failure... I tried reseting the CMOS without success.

Is there a way to omit the POST test at boot time? Why, when it manages to start, everything is ok? May this be a false positive?

I run diagnostics test after it booted successfully once and all tests passed.

Ps. My warranty has ended about a month or two ago :(