[HTC One X] de4life:
I thought I'd share my experience with this, as I've seen posts in the past relating to a water damaged phone boot looping and I don't think I've seen a proper solution given.

First thing's first, this advice is in relation to a very specific type of boot looping. Nothing to do with rooting, or software bugs. This is boot looping that has come about as a result of water damage. It may not have been long, maybe a couple of seconds in the toilet or some brief rain exposure. Whatever it is, you know your phone has been exposed to some water and it has begun boot looping. There will be no way to get out of it, as the phone boots for 2/3 seconds max before looping all over again. Even when you go into recovery, same thing, automatically boot loops.

Most people, including the official HTC Service Centre, will tell you the motherboard is fried and needs replacement. Whilst it is possible that may be true, it isn't guaranteed. It's an easy way out for HTC, as they can charge you an extortionate price for a new motherboard and not have to bother going through the work of taking the phone apart to find out what is wrong.

The solution may be much simpler - the Power Flex Cable. This is a very small cable that goes along the top of your phone. WHen water damaged, this cable can become damaged, causing a constant boot loop. The reason being it constantly tells the phone the power button is on, causing a constant on/off cycle. In this instance the motherboard is fine and you can get a replacement Flex Cable for less than £5!

There is an easy way to tell whether the Flex Cable is the likely cause of your looping. When the phone is looping, hold down the down volume button only. Don't touch the power button. If your phone still goes into recovery (then loops again) then it is entirely possible your Flex Cable is damaged, not your motherboard.

Next step, order a Flex Cable (they are easy to find). When it arrives, you will need to open your phone (there are guides on YouTube for this), detach the motherboard and replace the Flex Cable. An advance warning, this isn't easy and you have to be extremely careful. One bad move and your phone is history. The motherboard is delicate. If you look around the internet you will find guides which show how the HTC One X is configured. Note that the Flex Cable is behind the motherboard and quite awkward to get off. I would post a couple of links but as a new member I'm not allowed! PM me and I'm happy to share some helpful links though.

You'll know quickly if this has worked. When connecting your phone it will no longer loop. Let it charge for a little while, then power on and hope for the best. If the Flex Cable was the problem your phone will reboot, and you will be able to use it and get your data off.

Note that water damage can have long lasting effects on a mobile phone. Whilst this may solve the problem for a while, it's entirely possible your phone will fail at some point down the line. Prepare for that and make sure you back up accordingly. The above advice may give you a lifeline in getting data off your phone, though, and being able to use it for a little longer. I know that when I was looking around the net I only found this advice by chance, and I think it was on a non-phone related forum. This advice may exist on the forum somewhere but if so it isn't so easy to find. I hope somebody may come across this topic when trying to fix their water damaged phone and find it is the solution.

Good luck!