how to reinstall google play back onto my mobile How can i get the play store to work on my samsung galaxy ace it has changed to market. I have tried to download  it from the web but still will not work
Assuming you are rooted, installed a custom ROM and/or have a custom recovery, you can re-install "Google Apps" by flashing a GAPPS zip file.

The following website has ZIP files that you can flash in your recovery for most (or all) Android versions. https://basketbuild.com/gapps