and this is all what i need to power it?... i don't have 2.5" optical and hdd drive. mines are 3.5"! this is a problem?.
There are no 2.5" optical drives that I'm aware of.
IF there were, we'd lose a lot more CD/DVD discs.
You need to determine your total power draw for the PC. There are a number of power calculators available on the web. Google for it, plug in your information and get a rough idea as to the total power draw of your system.
Use that information to choose a PSU that will meet your power requirements and not break the bank.
And yes, all you would need is an ATX-compliant PSU. A 3.5" drive should be no problem, as long as the total power consumption is within the limits of the PSU you choose.
Have you looked in the FAQ yet?
How about the Wiki?
Under normal circumstances, a signature would go here.