Hello,
We need more details on the problem, be as specific as you can.
Any actual errors, or just performance (frames per sec) is disappointing?
What games are you playing?
A 77xx is not one I would recommend for extreme gaming with high settings on.
Running 2 monitors, yeah that would be a stretch for a 77xx with a current FPS shooter or MMO going on one screen.
I wouldn't try to Crossfire two of them either, better off jumping to a higher tier, and a better PSU if needed.
Unless it's a higher quality motherboard, usually the extra PCI-Express 16 slots are NOT allowing full use of all the lanes, varies greatly board to board.
See hwcompare.com to shop a better card, you would want across the board 50% better performance at least, imho.
Also visit here with help on filling in your specs, video card is not the only factor: CPU/Chipset/RAM
http://www.sevenforums.com/tutorials/180324-system-info-see-your-system-specs.html