HTC one screen extremely low brightness?

[AC Question]

Hello, I bought an htc about 5 months ago second hand and all was working fantastic until I brought it with me to a festival. So I didn't lose it I left it in the tent for around 9 hours before coming back to the screen being completely black but the phone still on, the alarm went off for hours and I was able to disarm it as the screen wasn't visible. I then thought maybe it was water damage so left it in a clean towel in my bag over night and when I turned it on again the next morning it worked perfectly but only had 6% battery and evidently died. I then left it at a charging station and when collecting it, it again worked perfectly however once it died again the brightness has never returned. I can't remember when it died or if it just knocked off but now I can just about see shapes moving on it and almost impossible to make out words and letters and application whereabouts. I've searched a lot online and have came across nothing that helps. The phone is actually working but the screen is as if it is on 0.05% brightness. The last thing I want to do is have to take it apart, not that I am not confident in doing this it is just a lot of hassle but can go there as an option. I would also like to try keep a lot of my stuff including pictures etc but if a factory restore would fix it I will go ahead and do that but I have no idea how to as the screen is to dim to see what I'm doing. Any solutions or ideas? Thanks a lot! LDoco