Chosen Solution
I dropped my Lumia 730 (RM-1040) in a puddle of water, and since then whenever I try to boot it up, it boots up, works for a minute (doesn’t matter if I use it or not) or so and then reboots. I am able to charge the battery through a universal battery charger, and I can confirm that when the phone boots up and I can see the battery percentage. I have been able to do a factory reset and during the process (which took about 7 to 8 minutes) it never rebooted (if it got to the reset progress screen in time). The display and the loudspeaker have been replaced once, before this incident, but I had no issues with that that. I have no idea if I should try to repair this or get a second hand one, and I really would appreciate some advice. It’d be great if it were possible to pin the problem, fixable or not.
It may be toast. I dropped my old iphone 4 in dish water. Immediately pulled it apart, removed the battery and dried everything I could. I then got a bowl big enough to hold the phone in about the middle, then poured rice in the bottom, put the open phone in and covered it with the rice.(I used brown I guess any kid would work) I left it in there overnight and then put it back together. Who knows it may just work, it did for me that phone still works and that was 4-5 years ago. I know not a technical answer but I got lucky!
