A 'Wackelkontakt'? You mean a loose contact? (Thanks Leo.org)
I don't think so...
But to my Boot-Problem: I think, when the PC off a while (while night o.s.), it boots nearly every time. Hm..?

P.s.: @all not-german: "Wackelkontakt" is a loose contact. Remember this, when you ever be to Germany - very useful ;-)