Constant DCs

I just got a new computer (Windows 7 64 Bit) and I'm constantly dcing. I can't even stay on for more than 15 minute without dcing. T_T
I'm new to Windows 7, I've been using XP only until now. Can I get some help please?
Also after playing for about 5 minutes, my desktop is automatically changing resolutions (1680x1050 > 800x600). It just changes by itself when I play MapeStory. Is there a way for me to change the settings for that so it doesn't keep changing? =/

Edit: And everytime I dc, I get rollbacked. Is this happening to anyone else?

since you got a new PC, are you fully updated on everything? Drivers, directx, etc?

I recommend not updating your ethernet/wireless drivers.

But even then, there were constant DCs a few days ago. There are fewer DCs now. However, your desktop changing resolutions by itself is a video driver problem. When you are out of the game, your video card should take a tiny bit of time putting the entire desktop on the 'native' resolution. It not doing this is a bug, and I'm hoping it was resolved in the latest drivers you have.