Hi!
As for upgrade reason, I've had to dismantle my desktop PC. After upgrade (RAM & Dideo I/O: no prob's) for unknowed reason, only my seagate 160 Go P/ATA accept to works now... My Samsung is recognized by the BIOS but after IDE port initialization (Smart available and OK!) the POST hung : no way to enter the bios set up... The problem occurs as well in master or slave mode. I feel realy disapointed as this drive is a brandnew one , and I would like to know if there is a way to solve my problem:
Many thanks for any help!
Regards!

The 250 Gb is new and recognised ? Maybe you have to update the BIOS to recognise drive larger than 160 Gb.
Try this first.

First of all: thanks for your kind & fast responce!
The Bios is up to date, and the drive was working before my attempt...Windows XP was on this drive and Linux Kubuntu on the other. I've also an USB2/IDE adaptator and this drive is not recognized too using this interface