Try doing a clean graphics drivers install, remove current drivers using Driver Fusion or Driver Sweeper in safe mode and install latest drivers from Dell. Also check if you laptop is overheating, they get moody at high temperatures.
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Intel I7 3770K @ 4.5ghz, Cooler Master Hyper 212 Evo, Gigabyte Z77X-UD3H, Gigabyte HD7970 ghz edition, 4x4gb Kingston HyperX Beast 2133mhz, Seasonic Platinum 860, OCZ Vertex 4 128gb, WD Black 1TB, WD Green 3TB+1.5TB, ASUS Xonar Essence ST, ASUS VE278Q, Windows 3.11