Broken app store

I realised a few days ago that App store won't open. I've tried everything and now I'm pretty few up. When I click on app store it 'bounces up' once and that is it. I cannot find anyway at all to open it! I have a 2014 mac book air and am on OS X Yosemite and can obviously now not update apps purchase any etc! If any one can help I would be extremely grateful! The funny thing is I discovered this after iMovie had a minor fault (still can't find a way to fix it) and decided to look for an iMovie software update etc then realised App Store wasn't working! Since I only just got a replacement iPhone after mine stopped working I'm pretty fed up of apple! Again I'd be grateful if some one could help!!