I did a small upgrade on laptop from Celeron M 380 to Pentium M 740. After first boot system detected new CPU, but system wansnt able to boot from any device anymore (HDD, DVD, USB). I checked BIOS, did load defaults, reboot, nothing. Then I ran built-in Dell diagnostics and it failed with error code 1000-0123. So I ran Memtest and somehow it booted off from CD, but hanged with OK e820 displaying on the screen. I tried booting with only one memory module, but symptoms remained same. Occasionally I get this on POST: "Memory write/read failure at 1118A000, read 640618F7 expecting 18F718F7 Decreasing available memory Strike the F1 key to continue, F2 to run the setup utility" Then I re-installed my old Celeron M and everything was fine again - system was able to boot normally and no memory errors were reported. I put Pentium M back and system was broken again. I'm confused, because I can't thing other than faulty CPU itself..? Full system specs: Dell Latitude 120L Intel Celeron M 380 (originally) and now Intel Pentium M 740 Intel Express 915 chipset 1.5 GB DDR2 RAM (1GB + 512MB modules) 80GB ATA hard drive DVD-combo drive Any advice would be appreciated.