Check your power supply first, to either peg it or eliminate it as the problem. Grab a multimeter (if you don't have one, go to a place like The Source or an electronics shop and get one: they're cheap and come in handy), set to DC Volts, plug in your computer's adaptor and touch the meter's probes to the end, one inside the cylindrical plug (that goes into your computer) and the other to the outside of it. Should read the voltage that your supply is rated for (look on the sticker on your supply) and the voltage should be steady and unchanging. If it does then unfortunately the problem is more likely with your computer.
Just for assurance set the meter to AC Volts and stick the probes into the outlet on your wall. Again should read a steady RMS voltage of 110V (+/- few), and this should not change either with time.
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G74SX-CST1-CBIL, i7 2630QM 2GHz
32GB DDR3 RAM @1333MHz
GTX560M 3GB DDR5 (192 bit)
17.3" LED 1920x1080
Sentelic TP, BIOS 203
Debian Linux Wheezy (Testing) Kernel 3.2, NVIDIA 295.40