S4 major problems please help

I've recently gotten an S4 gti9505 that was encountering problems with connecting to my network, I tried to fix this by flashing an official lollipop firmware onto it as I read this might have helped and since then I've had even more problems. I've lost my imei number and baseband. now wifi wont turn on and I'm getting to my wits end. I have tried multiple ways to fix this but so far I haven't been successfully any help would be greatly appreciated. Thanks in advance. also it will enter service mode but it wont load