I bought an Ultra ATA/133 PCI controller card to unlock the full capacity of my Maxtor 250 GB HD, and after I installed the controller card, I turned the computer on and got an error at the boot-screen that says the controller card isn't being initialized. I bypassed the error at first to install the driver for the card anyway, but everytime I reboot it's still there. I've tried downloading & installing Windows XP SP1 to address this problem, but it didn't fix it either. I've tried switching the controller card to a different PCI slot as well, but same error.

Does the computer work? If yes, just let it be - it's not a real error. If not, then you have to look in BIOS setup to enable booting from off chip IDE controller. I think HPs have an option for that under "Boot" settings. Disabling the onboard IDE controller altogether wouldn't hurt either.