My Macbook Pro keeps freezing and crashing!

Hello, I've had my MBP for a year and seven months (as of April 2014). At the beginnings of March 2014, it began freezing, showing these flickering horizontal lines and squares, and then, I had to do a hard boot to get it to work again. Back in March, I wiped the hard disk and reinstalled the OSX (Mavericks). There was no problem for about three days. Then, it started happening again. I took it to an Apple Reseller (as I live in Dominican Republic and we don't have apple stores, etc.) They spent about a day with it. When I picked it up, they said they reinstalled the OSX. I told them that's what I did, but as I'm young, they said it was different when they did it, yada, yada, yada. Through the entire month of March, I took it 4 times, where they claimed nothing really happened when it was with them, so I gave up on taking it to them. I just kept using throught the crashes as I am in school and I need it. I noticed the freezing usually occured when I moved it around (I use it for HS so I obviously need to go from classroom to classroom). I began to be extra careful when moving it and the freezing started ocurring less frequently. Tonight, I booted in Safe Mode and moved it around a lot, without being extremely careful about (so how a normal person carries it). The freezing hasn't happened yet. I'm currently typing this while in Safe Mode. However, I do not know what's the problem because I already reinstalled the OSX, and didn't transfer any Applications or Documents. I seriously don't know what to do anymore.

Can anyone help me with this? Please don't suggest I take it to Apple, because they haven't been helpful at all. I resetted the SMC and the PRAM, and the problem stopped momentarily. Also, the freezing is intermittent, so it can be perfectly okay now, and a mess later. Also, sometimes, 3 beeps can be heard and the laptop just doesn't turn on at all. Both RAM sticks were tested, and both are working perfectly.

Please, please, I AM DESPERATE and I will be forever in debt to anyone who helps me solve this.

PS: If I have to open anything, I can do it if you provide me with clear instructions, and please tell me if it's really complicated as I'm only 15, and I cherish my Macbook too much to do anything too hard myself.

PS(2): It has had problems in the past, so the screen 'cracked from the inside', so that was changed, and the logic board was also replaced, all in warranty, of course.

MBP 9.2, OSX Mavericks, though originally came with Mountain Lion.

Applications installed: Photoshop and Illustrator CS6, Spotify, Skype, VLC and BitTorrent.

THANKS IN ADVANCE TO EVERYONE!