Problems with my Samsung SII

Just some background - US Cellular is my carrier. Bought the phone about a year ago. A few months into it my motherboard fried and they (Samsung) fixed it. Now these are the issues I'm experiencing starting last night - the phone turns itself off and on, off and on, off and on, etc - I finally took the battery out. When I try to turn it off, it turns itself right back on. I was reading a book on my Kindle App and this screen popped up and had some kind of Samsung Privacy Agreement. I clicked yes because it wouldn't let me do anything else. Then some weird blue screen popped up (it was a background, like mine had changed or something) then another screen popped up - another user agreement but it didn't say Samsung so I declined it. Then my phone started going off and on, off and on, off and on... ETC. Could it be an app or something??

Please help!