oy, now i'm wondering if that power supply has a gray housing on it. no mfg and power data labels sounds like it's a used oem component, and if it is an oem part, it would be underpowered for anything resembling a medium or high end video card. it should have a label that shows power ratings in watts, volts and amps.
that system could use more ram too. 4gb on win7 64bit is low, especially for gaming. by the time that system is done booting up, it's using 900mb to 1.5gb of ram, depending on what you have loading on boot.
without spending a ton of money on the system and ensure it will to run ah fairly well...you're going to want to put 8gb of ram in it, either a radeon 7850 2gb or a gtx660ti 2gb video card, and a min 550 watt power supply.
*note* only look at seasonic, thermaltake, corsair (builder, enthusiast, professional series), and some select xfx power supplies...