The computer randomly restarts, what could be the matter?

Question

ubuntu

With some regularity (sometimes several times a day, sometimes less often), a spontaneous reboot of the system occurs, after which, reaching GRUB, the computer goes into an endless reboot. If at the same time you go to the BIOS, the reboot stops (the temperature of the processor in the BIOS is shown within the normal range). If the computer is turned off and on again, everything loads normally and continues to work. I checked the memory with memtester, no errors.
Installed Ubuntu 12.04 on ssd drive. I thought maybe I screwed up with the mounting.

cat /etc/fstab

# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    nodev,noexec,nosuid 0       0
# / was on /dev/sda2 during installation
UUID=684124c3-9527-4c93-bd9a-b6ebba89c55f / ext4 errors=remount-ro 0 1
# /boot/efi was on /dev/sda1 during installation
UUID=F452-3AE2  /boot/efi       vfat    defaults        0       1
# /home was on /dev/sda3 during installation
UUID=a52aa00e-bf27-4083-91b4-4d4b27f9beb9 /home           ext4    defaults        0       2
# data
# ====
UUID=2804122d-0550-4427-972e-ea4b4ecbff4f	/media/data	ext4	defaults	0	2
# tmpfs 2
# =====
tmpfs	/tmp	tmpfs	defaults	0	0
tmpfs	/var/cache/apt/archives tmpfs	defaults	0	0
tmpfs	/home/user/.cache	tmpfs	size=200M	0	0

I would be grateful for any ideas.

Answer 1

With a disk and an SSD, I can't say anything. If you can't find anything with the disk, then I would check the memory with both memtest86+ (boot disk. ie) and memteres from Ubuntu.
The last - under load, on the CPU and on the disk. Under cyclic load on the disk.
There are memory voltage drops, it happens (often) that the motherboard overclocks something without the knowledge of the owner, there are problems with the PSU - memtester is good for this.
Sometimes purely broken memory - memtest86+ is good for this (all the more so memtester cannot test all the memory, including in which the linux kernel)

Answer 2

Sounds like a hardware problem. The system config is needed.
Check the PSU, capacitors on the motherboard, video card.