When a system hangs at boot, it could be an issue in the bios setup or a hardware issue.
When is the last time you tried cleaning out the computer case for dust? If its been a while, you might want to take a look inside.
If you see any dust build up specially on the processor fan and heat sink, its time to do some cleaning.
You may also have a BIOS setting that has changed, or your CMOS battery may have died and your BIOS configurations were reset causing the system to hang.
If your CMOS battery has died, you will notice the time and date are incorrect in your BIOS setup utility. Replacing the battery will correct the problem.
Sometimes the BIOS is defaulted to a setting called HALT ON ALL ERRORS, changing this setting to other options, helps locate a problem like keyboard failure, you may also have a loose keyboard or mouse connector.
Are you hearing any system beep codes? If so how many and at what sequence?
These are just suggestions you can try, if they fail to solve the problem, I would have to ask did you change or add any hardware recently? If so, try removing that hardware and see if the system boots again successfully.
Good luck and keep us posted.
Please take notice. Oreo and I will not be available until June of 2012.
Thank you for understanding my absence, it is job and college related, so all is good. If I do not answer your PMs this is the reason why. See you all soon!
Bruce.