"blue screen indicateds a hardware failure" Not likely. Also, none of that power cord swapping or resetting PMU is related. Your OS isn't loading fully. The blue screen is the perfectly normal background that would be seen at the user login except Apple provides that lovely Aurora picture that covers it up. Your user login isn't loading. The system is hanging there. There is no quick fix. Try these steps in order:
-- Restart while holding the shift key for 30 seconds. If that doesn't work, skip ahead to"Boot to the OS X install DVD...".
-- If that works, restart again without shift. If that works, your done.
-- If it worked with shift, but it fails after that without shift, troubleshoot Login Items.
-- Boot to the OS X install DVD. Go past the language choice. Open Disk Utility. Repair the Disk. Quit Disk Utility, and restart.
-- If that doesn't help. create a new admin user account like this:
Boot to single-user mode (hold ⌘ and the S key for 30 seconds at startup).
Type:
/sbin/mount -uw /
Press Return.
{Nothing appears to happen, no problem.}
Type:
rm /var/db/.applesetupdone
Press Return.
Type:
reboot
Press Return.
{Now stuff appears to happen.}
[All typing commands require strict adherence to the exact spelling. This includes noticing where there is a space between characters and where there is no space.]
You may see the language choice next (varies with... too much to explain). You will finally get past the "Welcome" in a dozen languages and then you can create a new admin user. When you have the network choice, you can skip this and do it later, thus avoiding the registration process. Registration does not affect your computer or your use of software. The screen that follows immediately after you enter your name, address, phone (required), etc. shows your automatically generated "shortname". You can change this now, but not later, so change it! The shortname for this new account should be different from that of your old user. In OS 10.5 and older, you come to the registration a few screens later. Just choose "later". It doesn't come back later to nag (with OS 10.6, it is difficult to avoid registration unless you skipped the network setup-- no matter what, it isn't related to authentication like with Microsoft or Adobe).
-- If that fixes it, you can ask another question about how to migrate the old user's Library to the new user. Don't just copy everything over.
-- If that didn't help, boot to the OS X install DVD, go past the language choice, and reinstall OS X.