Prusa i3 heated bed issue

Hi, I'm kinda new into 3D printing, and just when I was getting successful prints with ABS (no warping finally) something happened with my bed.
After couple prints temperature started decreasing, after inspection I find out the wires came lose from bed, so I solder them, but after couple prints (bed temp: 100-110 C) same situation. And now I cant even get temperature to 90 C because solder just pop out from bed.
I would just buy new bed but if it's short circuit or something else I will just waste my money.
My printer is an acrylic version from china, bed is just aluminum plate with some kind of mat glued underneath.
If you need any more details (with you probably do because I'm newbie so I don't know what might be helpful) just give me know, .
Any help will be appreciated.

Edit: I just realized, I might have create post in wrong topic, so if moderator would be so nice

Edited 1 time(s). Last edit at 03/22/2016 05:35PM by returnVoid.