iPhone 5s stopped working after ios 8.3 update

Hi guys

Help! I updated my iPhone 5s to IOS 8.3 this morning and now the phone has completely died...

I noticed earlier this evening that the Health app wasn't working properly (not recording steps) and Instagram wouldn't load any images pre-update. So I restarted the phone which worked fine, but the apps still seemed to have bugs so I left it for 10 mins and went back to it and it was turned off (had about 50% battery before this) and now won't turn back on! Have put it on charge and nothing, the phone is literally dead... Has anyone else had this problem and what did you do?

Eeek did the IOS update kill my phone?

Thanks

jp