No harm done and thank you for understanding
1: We now know that your OS is 32-bit which rules out adding a second 4GB stick, see attachment.
2: You are aware that a PSU upgrade is required - you must however determine which add on video card you will be fitting before purchasing the PSU, this to ensure that you have adequate power (includings amperage) on the +12V rail + to make sure that you do not spend more than you need on a PSU that is way more than what you need, see my canned text below to help with selecting a PSU;
Please note that there is one thing that is possibly worse than using a known poor quality brand of PSU and that is using one that is unheard of, for brands of PSU to trust and brands to avoid please refer to the attached links http://www.10stripe.com/featured/psu/brand.php and http://www.pcmech.com/forum/showthread.php?t=208143
PSU database http://www.realhardt...vos/Page541.htm
Before purchasing a new PSU it is advisable that you measure the dimensions of the present PSU and ensure that the new PSU has the correct power connections for the MB, HDDs, optical drives, FDDs or add on cards such as a video card if one is fitted.
Quality brands include Antec, Corsair, EVGA, OCZ and Seasonic.