BOOTLOOP

It really depends on what the cause is - conceivably it may not be fixable at all. But fixing it without a computer is going to be difficult.

If a factory reset doesn't fix it then reflashing the phone is all that's left (i.e. completely overwriting the software with a new set). That is best done using a computer - seriously. But if you really don't have one it might be possible, since you clearly do have internet access.

To reflash a HTC you need a ROM Upgrade Utility (RUU). These are normally distributed as Windows executables, but you can sometimes find them as zip files (extracted from the executable package). These are still best flashed using a computer, but older HTCs used to have a thing where if you gave the zip a particular (model-dependent) name and put it on the SD card then booted into the bootloader (which you have to do anyway) it will try to reflash it from there. I don't know whether current models, or even as recent as the M8 still have that, but that's the only hope without a computer. And of course you still need to find the right file for your phone, rename it and copy to your address card.

Then there's the compatibility bit. For an RUU to run, assuming your phone is not S-OFF (which it won't be unless it's been modified, and if you'd done that you should already know everything I'm writing), you need the following:

* Bootloader should be locked (default state unless you have unlocked it)

* The RUU should contain software that is not older than what is currently on the phone

* The RUU must be compatible with your phone's cidnum

The cidnum is a customer id number, where the customer is not you but the carrier or market the phone was made for (not the one you are now using it with, unless that is the same). You can find this using a program called fastboot on a computer (that problem again), or if you know what country the phone was originally sold in and, if it was originally a carrier-branded phone, which carrier it was sold through, we can use that information to work it out. You can find information about the current software on the bootloader screen (reboot while pressing the volume down key).

Then when we know that we can see whether we can find a compatible RUU in a form that doesn't require a PC to flash it.

Hmm, looking at your username I see something about cid 11111111. If you have set that cidnum (which is a special one that bypasses these checks, and requires S-Off to do it) it may be easier than I feared. But as I say, anyone who has done that should know this stuff (and must have access to a computer - there is no other way of doing that). Can you give us some more information about the phone, whether it is modified, and what you did to get it into this state? If this has happened due to something you did, like a failed custom ROM flash, there may be other options.

That's not enough information - there is more than one 16GB model and they do not use the same software. We need the cidnum or information that can be deduced from. Please also answer the questions in the last paragraph of my previous post.

While you are doing it, going into the bootloader (described above) and telling us everything it says there will be helpful. The top line includes the model number (m8_ul for example) and there should be information about the hboot version, baseband and some software version information. All of that will be useful.

Have you tried a factory reset at Bootloop?
You can do one with a specific physical button combination i cannot recall right now.