Not sure if this goes here but I don't see any other section where it would go really. About a week ago, I found a HTC One M8 is a creek when I was hiking. I took it out and when I got home I placed it in rice for about 2 days. When I took it out, the battery worked fine because of the charging signal. I let it charge for about 8 hours and the signal is still there. The screen won't power up. Any tips on how to fix the screen without going inside the phone? Thanks.
The charging light means little - chances are it's completely non-functional except for the charging light itself.
However, you could check if it's booting and just the screen is dead by connecting it to a PC and observing whether the PC detects anything. If just the screen is dead, the PC should still see it as an external storage device. If the PC sees a USB device, you may be able to check further into its health by connecting via
adb. However, keep in mind that these come in both Android and Windows Mobile varieties, and
adb isn't going to work with Windows Mobile (there may be a logo on the back indicating which).
As far as fixing the screen if that's the only problem, there's no way to do it without opening the device and replacing the faulty component(s). Search YouTube and the like for teardown guides. However, given the device's exposure to the elements, there could be more faulty than can be replaced. Screen replacements are typically done for cracked digitizers, while your device may have fried graphics chips, etc., and changing the screen would be an expensive, time consuming, and fruitless endeavor.
Finally, although I don't know the circumstances of your find, I would point out that the device's IMEI (or equivalent) can be used by the carrier to return it to the rightful owner. If it's branded with a carrier's name, take it to the nearest store for that carrier and they can easily look up who owns it and get it back to them. Just sayin'.