My phone freezes when I boot it up and can't get past the "Android" watermark. I have done a factory reset but without any success. The Android OS might have gotten messed up so I would like to re-install it, how it this possible?
There are some things we need to know before we can help you - most importantly what phone we're talking about. If you can also provide some background as to what you had done up till now and what you did specifically just prior to experiencing the first failure, that would be helpful. Is the phone rooted? What is the last ROM version you are running, and is it a stock ROM or a custom? Do you have a PC and USB cable to work with, and have internet access on that PC? Some other things to keep in mind... The battery should be fully charged before attempting any ROM flashing, so it's a good idea to place it on charge and leave it there until we're ready to tackle this.
I have first cleared/reset eMMC in factory mode, then did a factory reset and cleared cache from the Android menu. I have this fake Lenovo phone called "Lenovo S820T" which I bought on this site called Aliexpress, so I do not know the ROM version, and I do not think the phone is rooted. I have a USB cable that connects the phone to the PC.
OK, so I am not familiar with that phone specifically, and given that it's a knock-off we may have great difficulty in finding the proper ROM for it. Without several pertinent pieces of information identifying the right ROM may be impossible. We would probably want the serial number(s), and if at all possible the exact model number however in the case of "replica" phones even the model numbers can vary from production run to production run, and the ROMs they are slated for can also differ even between several varieties of the same model number.
It is clear that Lenovo never made a model number Lenovo S820T. There isn't much information about it out there, but what is out there clearly slates it as a non-existing Lenovo product and so a knock-off. I don't know what else to tell you. Unless someone else out there has the same product and can dump the ROM for you, you may have no options left.