Proximity sensor not working

Hello everyone!

Hopefully somebody can help me resolve this irritating issue. Recently I had my iphone 4 battery replaced by a professional "techie" but since then my proximity sensor has malfunctioned. After taking the phone back he said he would try the tape resolution yet to no avail, he then footed me with a hefty cost to replace the sensor. Immediately declining his offer I decided I would take on this repair first hand, but need a bit of guidance first. After covering the sensor with my hand for however long, nothing happens whatsoever. So my question is, will replacing this sensor fix the problem or could it be more deep rooted. May I add that the earpiece also started playing up but after restoring the phone the problem has been solved. This did lead me to believe it could of been an issue with cable 3, but now I'm not so sure.

Any help will be greatly appreciated :)

Thanks