im not 100% sure that the psu is the problem but if that it is the route you want to go follow [guide|3225|this guide]. And you can buy a new power supply [http://www.ebay.com/sch/i.html?_from=R40&_trksid=p5197.m570.l1313&_nkw=ps3+slim+psu&_sacat=See-All-Categories|here on ebay]. again im not entirely convinced this is the problem but from the information you gave it seems logical to me.
Good luck and hope this helped,
Cody