Fujitsu-Siemens Amilo Pi 1505 Laptop HDD Upgrade not working.

Installed a NEW Toshiba SATA 250GB HDD. Fully formatted, installed Win XP Pro and OEM Audio/Video/Printer drivers.
Will not boot in Normal mode and runs extremely slowly and intermittently in Safe mode. The disk activity LED freezes for
long periods and it takes an age to respond to any user input, making it useless. If I refit the original 120GB HDD all works
normally. No BIOS changes made. The operating system and other software loaded on both drives are identical.
I had not expected any compatibility problem but it appears there is such an issue. What am I overlooking? Has any other
of you guys had such an issue and what is the remedy? Do I have to make Bios/Chipset alterations?
I would be very grateful for any suggestions or information. Thanks.