I'm guessing you are the oldest child? I know it is a big cliche, but puberty is a very tough time. Not for the person going through it, man, why does it always have to be about you

It is a very tough time for parents. You may not notice the shift in personality as much because, well, the change is happening to you so you are unlikely to notice it. Your parents, on the other hand, have to deal with essentially a whole new person. You probably don't believe me, but trust me, that is the case. So they are wondering: "Who is this stranger in my house and what happened to my son (or daughter, but this is a video game forum, so I'll bet heavily on the male demographic)?" Understandably or not, that leads to a certain amount of "freak out" on the part of the parents. Sometimes, that freak-out manifests itself in the form of new rules, strange dominance games (my house, my rules!), and a great deal of apprehension.
On a related note, out of curiosity, what is your social life like? You said you got good grades, but what about the other life skills that school teaches? I know it sounds crazy, but if you are excessively nerdy (straight As plus positing on the Bethesda forum suggests that may be a realistic possibility) they may be concerned about your social development. That may mean that they either don't like the friends you do have (a likely possibility given the draconian bedtime) and want you to make new ones (hence summer school, which creates unlikely friend-pairings due to shared misery).
Or maybe they've just noticed that you've been more isolated lately, so they want to get you off the electronic distractions and back into a meaningful social sphere. They probably don't have a good idea as to what you are "into" beyond the video games/internet that they want to wean you off of, but they do know that you do well in school. So they want to place you in a semi-social environment where you are not only comfortable but also likely to succeed. That is because, as an advlt, most friendships start in need. For example, I live in an apartment and needed a cool basemant for brewing. I kinda knew this one guy who had a house. So, I asked him if he wanted to brew with me sometime. I show up in my piece-of-trash car and during the brew-day, he mentions that he is a big gear-head. I taught him how to brew and got to use his basemant while he taught me how to fix up cars. And we became good friends because of that time together. The problem is that friendships in middle and high school don't really start that way -- especially if the excellence in question is in academics. But parents forget that sort of thing. So they are trying to do right by you and place you in a situation where you will succeed but because they have essentially forgotten the byzantine rules of middle and high school and they don't really know you anymore, they are going about it in a completely backwards manner.
Not to cause any freak-outs on your part, but "inappropriate sites" were also mentioned. If they were run-of-the-mill porm sites, that just compounds the problems of having a child who is undergoing puberty because it forces a very visceral confrontation with that fact. But if they were "different" in any way, then that may also cause them some distress. I've got a bit of a sweet-tooth for the [censored], and I was around your age when my parents found an unsent letter to a friend expressing my feelings. I didn't know they had read the letter until some three months later. But that time was amongst the worst of my life. Not just because my parents avoided contact with me (including freakin' eye-contact) but also because what little contact there was consisted of arbitrary new rules, yelling, and all manner of nastiness. And I didn't even have any idea why! I'm not saying that is what they found in your case, but if your parents found something like [censored], that would certainly count as "different" and in the way that would make parents deeply uncomfortable and confused. Sure, [censored] is essentially harmless. But we are posting on a message board, we know that sort of thing. Chances are, your parents don't. Misunderstandings like that can really compound the problems I've mentioned.
Basically, parents are like any other person. Identify and address the underlying problem and you'll be able to solve the situation. I'm guessing your age, your birth order, and your changes have a lot to do with it. And for that, I am sorry because there is really nothing you can do. But see if you can identify anything else on top of those that would be compounding the situation. If there is something like that, see if you can address it. If it is an important part of who you are, confronting them about it (in a respectful manner) is your best option. If it is unimportant to you, change the behavior and see what happens. If it is a misunderstanding along the lines of "[censored] as a porm site, OMG, my son is into the wildest fetishes imaginable!", then confronting them about it in a jovial manner is a good call. Along the lines of "I think I know what is freaking you out and, let me assure you, it is a big misunderstanding!"
Good luck, hope this helps!
Edit: Hmmm, they appear to censor a very popular website here. That makes sense, since this website is known for being obscene. Think of the lucky number associated with clover and an familiar Japanese form of address. As for the other censored, well, I'll let you use your imagination.