what about the 250w?

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No, it needs to be at least 450.

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what will happen if i was to use it?

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Could pretty much fry your entire pc, dont do it.

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"...and a Roswell 750w Power Supply" It's Rosewill which is Newegg's "house brand". Rosewill doesn't manufacturer PSU's, they're a reseller. Is this the one you bought? http://www.newegg.com/Product/Produ... You could have done a lot better for a lot less money. PSU's with multiple +12v rails should be avoided. Here's a better 650W unit for a lot less money: http://www.newegg.com/Product/Produ... And here's some useful info about PSU's: http://www.pcpower.com/technology/m... "so it could just be too much power..." No, that has nothing to do with it. You could have a 5000W PSU but if your system only requires 400W, that's all the PSU will produce. See the above link. "what about the 250w?" Not gonna get it done. If it works at all, it will become overloaded & possibly fry your new video card or worse. Does the old PSU even have the necessary plug(s) for the new card? Don't chance it...pull the new card until you get the PSU replaced.

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what is multiple rail/ single rail? i am a newbie!!!

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I'll try to keep this simple...a rail is the same as a circuit. Some of the most important rails in a psu are +3.3v, +5v and +12v. The +12v rail is the most used in a modern computer and it's used a lot...by most everything. When power hungry processors (cpu's) appeared and video cards became more and more power hungry, psu manufacturers has two choices to meet the increased need of +12v power. 1. Build a psu with one very strong +12v circuit or 2. Build a psu with two or more normal +12v circuits. In example 1., you just simply plug everything in and go about your business. In example 2., you would need to balance the +12v loads manually. Something like Motherboard/CPU on +12v_1, video card 1 on +12v_2, and video card 2 on +12v_3. So example 1. has a single 12v rail and example 2. has multiple 12v rails. Skip

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but you would think with this dispursement of power would be more power effiecent and would cause more centralized faults rather a massive power failure...

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I gave a simple outline of single vs multiple rails. It gets more complicated...look at the label of your Rosewill psu. You have 4 12v rails of 18a each. 4 x 18 = 72 right? Wrong! 4 x 18 = 54 So, do you look at it like you have 4 18a rails or 4 13.5a rails or 3 18a rails or 2 9a and 2 18a or 1 12a, 1 6a, and 2 18a or ? Confused? That's intentional...both by me and the psu manufacturers. Skip

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