http://www.tomshardware.co.uk/forum/247863-10-dell -optiplex-gx280-upgrade-question

toto je pre teba dôležité:

Try updating BIOS to A08 rev. I dont know what series was my previous cpu, now im using 650 so 6x0 are supported. http://dell.driversdown.com/dell-d [...] 1631.shtml is the link with BIOS update. Try it

I think there is a trick in Dell computers...
only Pentium 520-540 models will be work and all series 6x0

(but 6x1 will not work..) it is the whole truth..