Monitor freezing question

now, stop me if I'm in the wrong place to ask this question, but my sister has a Compaq laptop, I THINK it's a, uhh, 9000 series or something?? But anyway, the deal is she has the auto-hibernate turned on, so after about 30-45 minutes, the computer screen will turn off and the actual cpu will still be on, but as stated before, the monitor will turn off, until you move around on the mousepad or just interact with the computer, then the screen turns back on with the currently open/running files as they were before you left, though what's been going on lately, since oh, about 2 or 3 days ago, the computer screen will take 1-2 minutes to turn back on, sometimes it just won't turn on at all, and I'll have to manually restart the computer, in which the screen pops up as it normally does, and everything boots up as it normally does, so it's apparently not a problem with the programs, but with a processing error on the monitor, seemingly... But of course, I don't know this for sure, so if anyone could help shed some light on the situation, it'd be most appreciated, ya?