I've been limited not only from playing games on weekdays, but there was a cap of 2 hours per weekend as well. In addition, I can't use the computer for anything non-school related.
Luckily that's not the situation anymore. However, it happens, and what can you do? Parents impose such restrictions, hoping you would instead spend your energy and time in schoolwork or other activities. Video games have this reputation of being time-wasters, and they can be.
Unfortunately, I'm guessing most of the time this won't work out, because the kids will get angry, instead. You can try changing your mother's mind. This can be done by calmly reasoning it with her (arguing heatedly really doesn't help), and generally presenting yourself as a mature, responsible adult who knows enough to make sound decisions.
Of course, if that fails, you have some extra time on your hands. If your schoolwork isn't good, that should be number one. Take whatever time you need to properly deal with school, and worry about other stuff after dealing with schoolwork. And with your extra time, you might as well go out and get a job, read something interesting (trust me there is a lot of good stuff to read. unfortunately, high school fails to introduce students to it. you'll have to find them on your own), or pick up a hobby. For example, ever though that lockpicking and safecracking were really cool? Buy a couple books, a couple locks, and learn how to do it! That applies to programming/web design/electronic engineering/etc.
There's actually a lot of interesting little things a person can teach himself, but most ppl don't. :\.