Random reboots and no apparent reason

Hey everyone,

I'm experiencing some problems lately.

I got my Astaro on October, 7th. Until last friday, everything went great! But since then, I experience some strange reboots. The climax was on saturday with 5 reboots within half an hour.
The logs shows "reason unknown", that's it.

I know that there are many possibilities, but I want to localize the reason behind this, whether it's faulty RAM or an incompatible hardware.

Here's my config:

Mainboard (incl. CPU): Intel D2500cce
RAM: 2 GB DDR3 RAM
Hard disk: 120 GB 2,5" SATA
additional LAN NIC Intel PRO 1000MT
Astaro: ASTARO UTM9, latest patch level

I didn't find anything about my mainboard in the HCL, but I assume that is okay.

Please help me, it's annoying as hell.

Kind Regards

ZeroEnna