You could try and see if the aerial has fallen off the wifi bit. Somewhere in your laptop (probably easily accessible from the bottom if you take some screws out- the best thing to do is google for laptop model disassembly and there are probably lots of videos and pages about taking your model to bits) there will be a little card like:
Click to see full-size image. |

The arrows cunningly point to the bits that might have got disconnected. As John says you can probably get a whole new little card from eBay, but if you are getting some but not enough signal, that seems to be unlikely as a fix.