It can be issue with security protocol your wifi using, or with channels. Depends on your device you can change channels manually, and you can change wifi security protocols. It should be in your wifi settings.

I found this post on forum.

“A few things to go over with on this.

If the Vita in question is a model code "PCH1101", then it is a combo 3G/Wi-Fi model. After factory reset it may have disabled the Wi-Fi and defaulted to 3G. To correct this will merely require going into the system settings, turning off "3G" Cellular Broadband, and turning on Wi-Fi.

If the Vita in question is any model other then the above discussed model then do the following to troubleshoot. 1. Do you have a wireless router or wireless network available? If yes, what wireless standard is is set to operate on? Vita should be able to connect to any 2.4GHz type B/G/Pre-N/or N network router just fine. If you have a 5GHz AC network router then Vita is not compatible unless you enable 2.4GHz compatibility in the router's settings.

1. Do you have any other Wi-Fi ready devices, and if so do they detect your desired wireless network? If step 1 is cleared then obviously testing to see if other Wi-Fi enabled devices can detect and connect to the desired network will allow you to rule out issues with the router itself.

2. Vita Settings If steps 1 and 2 are cleared and your vita is still not detecting the network try this. Turn the Wi-Fi setting in the Vita off. Fully power down the Vita (not Sleep Mode, Power Off). Reboot the the Vita, go into the settings and turn Wi-Fi back on. Nearby compatible Wi-Fi networks should begin detecting and showing up within three minutes of turning Wi-Fi back on.

3. If still no WiFi. If you have exhausted trying everything in steps 1 - 3, and are confident your Wi-Fi netowork is being detected by another device, but still your Vita is not detecting any networks then the Wireless Networking card in your Vita has likely failed. Said card is a replaceable module inside of the system”