laptop goes black and shuts off

i have a Dell Studio 1555 laptop, modem ready w/ my Blackberry, and have Verizon wireless as we live in a rural area in Montana. 

only recently (since the Blackberry blackout) w/o warning my Dell Studio 1555 (2+y.o.) will suddenly go black and shut off. this has happened a handful of times this month.

i then cannot get the laptop to come on for awhile. i disconnect it from the plug as well as the Blackberry, and take out the laptop battery, and still nothing.  i wait awhile and do this again and may have to do it more than a few times, then suddenly i can push the on button and it comes on?

what is causing this? overheating? dust on the fan? could it be too because my Verizon Wireless Service at times is low to med low connection status as living in this rural area in NW Montana we have only one Verizon tower for 20 miles???

any ideas will help.....thank you