My play store doesn't want to work

[Ams]

My play store doesn't want to work it keeps saying no connection but everything else on my phone is working even galaxy apps are working. My phone just got back from screen repairs. So need to download all my apps. But I don't understand why it isn't working. The phone still has the old play store version cos hasn't been in use for a while. is there any way ii can update it altho it isn't working? its a s4