There are what looks like two tiny black cubes (marked 1 and 2 on the pic above). I probably overheated the solder holding them and now one of them is missing.
What is the function of this cube thing? Even with that cube missing, the computer boots up normally on windows xp and all devices seem to work.
Also the touch screen worked the first time I soldered the wires, but one wire came off and had to redo the solder. That’s when I damaged the thing. The problem now is that although the wires are properly soldered, the touch screen does not work. Is there anyting I can do to fix it?
The tiny black cubes are most probably surface mounted resistors. Not having one of these could easily cause the circuit to not work. There is usually very, very tiny printing on the resistor indicating specifications. I suppose you could just try to match the one on the other lead. Judging from how the two parts are installed, I would make a guess that both are the same value.
Four really big disclaimers:
I’m guessing the two resistors are the same – they may not be.
Obtaining a replacement resistor won’t be easy.
As you discovered the hard way, hand soldering surface mount components is really, really hard. Doing this requires a special soldering iron, a steady hand, and much skill. You should work under a magnifier and have very good light.
The traces on the board are fairly fragile. Every attempt at repair increases the probability that you will damage the board. You can also induce latent problems which may show up in the future.