Question PSU problem, RAM problem or Storage problem?

Aug 17, 2019
So, i try to upgrade some old PC back at home for my nephew. Bought it 8GB ram kit, and 120GB SSD for system. Works fine for couple of weeks, but then something happened.

It run fine, able to boot to windows quite fast (couple of second), but sometimes i can hear the buzzer from motherboard making low beep sound (just once, and quite). After that happened, the system seems freezing but i still able to move the mouse pointer, dragging window... But, i can't close or open new programs/window for 30sec to a minute, then back to normal.

I've tried checking disk for corrupt or bad sector at first, since i thought the beep sound came from hard disk. But the result turn to be fine. I don't know about power supply, or how to check if it's sufficient or not.

Now, the RAM. Things seems to be normal again after i pull and place the RAM, but after a while (days) the issue came back again. The quite beep and soft freeze.

I'm not a tech person, and Google seems don't help this time... So plz. Is there a way to test RAM from error?

The system:
Board GA H61M-SP2-R3
Pentium G620 (planned to I7 3770 or I5 3570k)
120GB SSD & 500GB HDD
GTX 650 OC (planned to RX 580)
450w PSU

I don't know the brands for the rest since i still away, but it's just standart stuff that you can guess. Oh, and it's 2nd hand stuff.