I just installed a 3.06Ghz, 512K, 533 Mhz, 478 pin processor in my DELL P4, 2.53Ghz which has an 850E chipset. I analyzed the chip carefully with a special utility first to ensure I bought the right processor.The instal went fine, if slow. Everything fitted and clicked home. Windows XP will not boot up now. I get to a blue screen that tells me that there is a problem and Windows XP has been shut down to prevent damage to my PC.I cannot see the whole screen (this is a separate monitor issue at present) but it has a partial string that readsVER_IRQL_NOT_LESS_OR_EQUALIt asks me to check any new hardware or software for correct installation.Can anybody tell me what is going on and how to fix this?I have posted at DELL too but I thought I'd ask here anyway.Appreciate any help, thanks!JS

This may be where Win XP sees your CPU upgrade as a major hardware change that is outside of what it 'thinks' is acceptable! Does the boot sequence proceed far enough to allow you to hit F8 and enter Safe-Mode? If it does, and will succesfuly boot into Safe-Mode, then you can uninstall and re-install motherboard drivers, etc, and then try rebooting into your normal configuration.If this still fails, or it wont allow Safe-Mode, then as far as I know, you're going to have to re-install Windows! You may be able to use the Repair Console (available when you start the re-installation process) if you can figure out what it wants you to do!! (I always have trouble with that as I'm not too clever with DOS!)Hopefuly Safe-Mode will do the trick.....

Is the CPU identified correctly by the mainboard BIOS?

Looks like you have an IRQ conflict. Have you started your system successfully in safe mode? If so, one of your pieces of hardware (sound card is the likely culprit) is in conflict and you'll have to uninstall and reinstall. I couldn't find anything on the Internet in regards to the partial error message you provided but you should try to get the whole/correct string and insert the string into a search engine and see what it means. That helped me once.Another possible solution is going into safe mode and uninstalling every piece of hardware (sound card, DVD drives, video cards, etc.) and see if that solves the problem. The drivers will reinstall when you restart in normal mode. I remember having a blue screen once and simply went inside my computer and unplugged my DVD drive and restarted. That turned out to be the problem and the system restarted without any problems after that.Hope this helps.Jim

Jim:It was precisely that: an IRQ conflict. That did it. No more "engineering" for me. I packed up the processor and am shipping it back tomorrow.JS