It all started when I replaced the Pentium D 920 (2 cores and 4mb L2 cache) with D 945 as I expected a better performance. Bios was 94610J.86A.0047.2006.
I resetted the Bios to default, but the problem remained. One core and 2mb L2 cache (insted of 4mb).
So I updated the bios using ts94610J.86A.0087.ib.exe booting from a usb stick. it worked, but did not help.
So I put back my old D920, but the problem persists.
I triied changing the setting in the bios core multiplexing back and forth, nothing changed..
Before I continue wondering, i asked the comunity for advice.
Geetings from Vienna