If you are still experiencing your WiFi problems, here is a couple of things to try.
1. Download a free WiFi scanner program (inSSIDer is one example, here is a link http://en.softonic.com/s/ssid ) and then use it to measure the signal strength of the networks that you wish to connect to. Or use it to keep an eye on the signal strength once connected to see if a varies. Remember the values are what your WLAN module is telling the software.
2. If the values are always low (the signal strength value is in -ve dB, therefore the higher the number the lower the actual signal level), I suggest that you initially check that the WLAN module's aerials (there are two) are firmly attached to the module. Here is a link to the service manual for your laptop, scroll to p.35 for instructions on how to access the WLAN module and aerials.
If you don't see anything wrong with the aerial attachment the perhaps then module is faulty. If you Google just the part number 676786-005, (found at the top of the p.35) you will get results for suppliers of the part. The price ranges all over, here is one of the cheaper ones http://www.notebookparts.com/hp-pavilion...
Hopefully this may be of some help.