|Do you have TWO power connections on the card? If so, do you have them both connected? |
According to the Manufacturers specs there are TWO 6 pin PCIe power connectors on that card.
According to the Rosewill specs for your PSU there are FOUR 6 pin PCIe connectors. They should be coming off of TWO different rails. If you currently have both connectors mated up, then try pulling off ONLY one and connect one of the 2 that were not in use.
Be sure the card is fully seated and the tang at the back is locked.
If the system still will not then you may need to either get another card or PSU. All the cards in that series pull about the same power so changing brands isn't going to help.
I assume the computer ran before buying this card? If not, then the problem may not be the card/ PSU at all.