The above solutions may work for some, but my fix was MUCH easier!!
I had this problem this week of no wireless networks being detected after having a Vaio VGN-C series for over three years now. I never had this problem before, but my toddler hit some keys on the computer one day and the next day my wireless internet wouldn't detect anything. There are several different posts online on how to fix it, including redownloading drivers, or simply turning the switch on on the front or side of your computer.

The real answer is MUCH EASIER! For some reason, Vaio put this link in the quick launch bar on the bottom right of your screen (You know all those anoying little things that you never use!?! ). Just click on the green box that has LAN in small print and check the box for wireless internet and you are good to go. There was no need to restart the computer or anything. I looked forever trying to find a solution to this and it is a simple fix. I hope this helps someone else out there who got as frustrated as me about this weird feature.

Here is a screen shot of what it looks like on my Vaio VGN-C190G: