WiFi Connectivity is probably the most common and the most annoying problem encountered in HTC One X phones. You will get this problem mainly if you have a Tegra 3 HTC One X model. When you try to connect to a Wifi spot, you will get no signal or poor signal, even if the router is very close. In order to see if the problem is present, you can try and compare the signal strength from two devices: the One X and another smartphone or laptop. If the signal is really poor on HTC One X and if you have a Tegra 3 model, then your luck run out... It seems that the manufacturers forget to make a strong connection between the mainboard and the Wiffi antenna. In order to test it, gently squeeze the back of the phone (the case), between the camera and the volume control buttons. If you'll see a boost in signal, then you have a hardware problem, and no software fix will help.
This is not a cheap phone, and I was not expecting this from HTC, but... it happened and we can do nothing about it. But, even so, what can you do? If your smartphone is still in one year warranty, you can try and send it to HTC service. Of course, they will try and convince you that this is not a permanent problem, and will try every trick in the book like check some options and so on. If you're out of warranty then you should try a fix of your own. You can and check the box for " Best Wi Fi performance" found in Wifi Menu -> Advanced. This should give more power to WiFi antenna, but it will also drain the battery faster, and your signal will still be weak.
How to fix HTC One X Wifi Problem
Let me start with this: DON'T DO IT YOURSELF! I know there are few videos on Youtube on how to open and fix HTC One X, but I've tried it for myself and I messed up the display so bad, I had to change it. And that was not all, you should read about my display problems here.
So, you must go to a professional GSM service in your city and ask them to gently open your phone and fix the WiFi problem using this video as a guide:
The display is really fragile and expensive, so be sure to mention that to them.