2.6.0-1/2 reboots out of the blue

hi,
every time I try to run 2.6.0test1/2, the first couple of minutes all went well, but then without an error or so, my machine reboots suddenly! I have an athlonxp 2000+ with kt333!
were can I find infos whats going on in that moment!

thanks in advance - thorsten