thanks for the quick reply!
I already contacted the very bad support at
http://www.globalscaletechnologies.com/. After 3 weeks they told me, that the warranty period expired and I could send it to them but I would have to pay for everything (shipping, parts and labor).
So, I guess I'm on my own here... From what I've read the PSU problem normally shows itself by a blinking power led, but I have a green led which is always on.