My old iPhone 5c won't turn on even though it was working fine a month ago and has just been in a drawer since. How can I get it working?

I upgraded my iPhone a month ago and have been experiencing problems so I need to get it fixed. It will be weeks until I get it back so I decided I d use my old iPhone 5c until then. But I can't turn it on, it was working fine last time I used it a mo th ago. I tried charging for hours and hours and holding sleep and home buttons etc and it still won't come on. My charger is fine. How can I turn it on?

Phone won't respond to touch?

I have an iPhone 5c and have had the screen replaced a few times. The last time was at the end of May/beginning of June and it's worked perfectly until now so maybe it's because of the screen maybe it's just the phone? I've restarted and rebooted it multiple times but it still responds to no touch or very little touch at at a time. I waved my hand over the screen, and it opened apps without me even touching it. When the screen does respond to touch it's only for a few minutes at a time and won't let me press certian letters on the keyboard

Grandpa messed up my iPhone 6s Plus when trying to fix the screen. Read details please how much would it cost to fix it. Pic in comments

I dropped my phone on the corner, and it broke the screen. Instead of just taking it in and getting it fixed, my grandfather insisted on fixing it himself in hopes that it'd be cheaper than paying $150. I had to agree because he bought me the phone for my birthday. However, mr. DIY didn't have a clue what he was doing except from some YouTube videos. And fix it yourself kit instructions. He bought the kit to replace the screen, for $40 and accidentally ripped one of the ribbons inside of the iPhone 6s Plus when he was trying to replace the screen. He didn't replace the screen back on correctly so now there's a little space between the frame and the phone at the top. I could handle the space though because my case would hide it. HOWEVER; the colors don't seem as contrast, and HD as they use to be. Also, there's a tiny piece of dust in my front camera where he decided to keep my phone wide open for three days and didn't think to make sure there was no dust inside before placing the non-cracked screen into place. I don't need a screen replacement but I'm wondering what they might charge at Verizon or apple to take off the screen clean the camera and place it back on correctly? Or would I just have to pay the $150 because of the color and a potential "wrong" ribbon issue? I've added a picture of the screen now that it's "fixed" in the comments.

Do I need credit to buy an IPhone 7 in down payments?

I'm 15 years old and I would really like to buy an iPhone 7 but I'm not sure if I need credit. I initially have to pay about $30 at BestBuy and pay about $25 each month for 24 months. This can be with T-Mobile, AT&T, etc. I just don't know if I need credit to be able to do this and wether it depends with what phone service company I chose. Any help will be appreciated and suggestions to which phone company to chose.