monitor help, its "out of range"

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so my gf apparenty wanted to change my setting on my computer to benefit her. so she goes to the properties and changes god knows what and now when my computer loads my monitor says "out of range". i rebooted it and i am currently working in the "vga mode". i tried to get my old setting back but to no avail. i tried rebooting again and it put me back at "out of range". can anyone direct me?