Computer temporarily unresponsive after sleep

Recently I bought an Antec 900 computer case. And now, whenever I wake up my computer from sleep mode, it is unresponsive for about 20-30 seconds. This started right after I switched to the Antec 900 case, and never happened before with my old case.In addition to this happening after waking my computer, I also have the same problem when booting my computer. When booting, on the screen that shows the Vista logo and the bar moving across, my computer always freezes. The bar on the screen stops moving and also my harddrive light on my computer stops blinking. After 20-30 seconds everything starts back up again like normal.I tried formatting my harddrive and reinstalling Windows Vista, but that didn't help.Is this a problem with this case or could something else be causing it? Other than switching cases, the only thing I can think of that changed is that now my 2 hard drives and my dvd drive are all connected to the same power cord. Could this cause it?