Alienware issues after switching cases

Hey all,

So recently I decided I wanted a bit more room to upgrade some of my parts more. I moved my Alienware x51 (I believe the first model) into a new case, with a new PSU/new cables and all the works. When I start the computer now though, an error pops up saying no power sensor is detected, as well as the internal disk drive not being detected. When I go into my BIOS, it seems like the computer recognizes the HDD. If I turn off the error messages, the computer boots, but skips the Alienware logo. Somewhere randomly after starting up, the display stops getting signal, but whatever was playing is still playing/the sound still works. I've tried rolling back the graphics card driver, to no avail. On the HDD front i've tried reseating several times with several different cables, but it only works if I were to ignore error messages on start up. In the ePSA, the hard drive also has issues. Not really sure what do to in this situation.