Mac Pro won't fully boot

So I figuered out the Lion download and it installed fine on the new drive it restarted and....would not fully boot the computer. Same issue, grey screen.....all that work no joy.

A computer geek friend at work suggested it has something to do with the "boot loader" and that it has been corrupted and fixing this involves going in the terminal and typing code. I'm getting a bit distraught can anyone weigh in you've all been most helpful. Really don't know where to go from here.

I installed Lion on an older PATA drive in an external enclosure and it's the same problem will not click and finish the boot. Apple screen appears then dark screen then spinning ball on top of dark screen. I will try the NVRAM test.

Tried the CMD-OPTION-P-R after powering on held until 2nd chime Apple logo>Grey scree. and spinning ball.....what hardware problem could this possibly be? A little backstory year ago I noticed some issues with rebooting to another drive in system preferences. I get this dddddddd-rrrrrrrrrr noise repeat and I'd have to use the power button to restart the computer since it was stuck in the process of switching to the other drive.