Mac Pro HUUUGE PROBLEM (POWER)

hi, i bought my MacPro in August 2011. it has a little more than a year. It is a 2.8 Quad-Core Intel Xeon. i changed my memory to have 12GB 1066MHz DDR3. I have Lion installed on it For the last 6 months approximately i had trouble powering up my mac. when i pressed the power button, it didn't lit up but i was hearing a click. thank 15 seconds later, an other click so i was repressing the power button and it was powering up just fine. But since Saturday night (i'm writing this as of Sunday morning) problems with my machine got REALLY WORSE. Since i'm building myself a new desk for my computer, i unplugged it on friday afternoon and plugged it back saturday night. When i pressed the power button, i powered up on the first time. WEIRD. BUT when i i tried to shut down it, i had a Kernel Panic appearing. So i forced shut down it while holding the power button. When i tried to re-power it, i heard the same click but NEVER the second one that was indicating me to power it like it used to do. so i unplugged the power cord, replugged it then it powered on. but again, on shut down, kernel panic. i did this on and on. So i decided to format my computer, reinstall everything. when lion finished installing, it asked me to restart, so i clicked restart but it never it BUT, the power light was on. So i forced the power off then it booted just fine. Tried a shut down, it went fine. Repower it, i heard a click. I waited, then i heard a second one so i did like always, POWER IT UP. it worked. but kernel panic is back on SHUT DOWN. Seriously, i'm about to take that stupid computer on a bridge and throw it over. I bought this computer 3150 CAN $. it over 1 year so i don't have a warranty anymore. Since, i didn't buy the apple care. So please, could someone help me with that. I'd be forever graceful.