You sound like my daughter.  We unplucked the computer and take away the cell phone at 11:00 PM and give her seroquel to help her sleep.

Don't know what else to do.  She just couldn't seem to stop.

I have Bipolar II Disorder and adult ADHD.  Stinks, doesn't it!!    I've had it since grade school, but was not diagnosed until I was 51.  I also have trouble getting off the computer.  I usually try to get all the work done for the day before I ever go to the computer room.  Like now I am starting at 7:30 pm.  I want to order from a couple places or at least check out their prices.

 Meanwhile, I have decided that it is imperative that I handle my e-mail every day. If I don't, within 3 or 4 days, I seem to have around 200 to fight my way through, which makes me feel overwhelmed--again.  And instead of being a pleasant experience (once I've gotten rid of the spam), it becomes a "thing I have to do"--not fun.

My big problem is playing games--this is coming from a senior citizen that never had Intellivision, Game Boy, Nintendo, etc., etc., although my 5 sons did.  I really enjoy certain games.  But I usually won't quit a couple of them until I win.  Not smart, although I still enjoy it.  But I am a night person and am retired so I can sleep in.  If not for that I would feel very guilty.  I was abe to limit myself as long as I was working full time but that's not an option anymore.

I find that if I set the timer on the oven for a certain amount of time, I do better.  At least I have to come up for air.  Sometimes when game playing, I'm so into it that I'm oblivious as to how much time has passed.  So I find a compulsory break  that makes me get up, walk down a hall and go into the kitchen brings me back to the real world.  I also just keep looking up one thing after another, not  only games.  Same thing happens, I just don't realize how long I've been at it, unless I have that necessary stop. I know there is a clock right on the computer, but that's not the same somehow.

 So you might try this idea, if you haven't already.

 I live alone, so I don't have anybody to yell "Go to bed" or "Get off the Computer" like I did before my last son got his own apartment.  That used to work very well, as we shared one computer.  Maybe if you don't live alone, you could ask another person to help you limit your time.  Tell them you 're going to stop after 3 hours or whatever.  Then they are to come , turn the computer off, and escort you to a different location.