Make my website work function on all browsers and devices

Hi there, I need someone who can quickly go over my site - www.guitarlessoncentral.com - and ensure that it looks correct on all browsers (maybe ignoring internet explorer 6) and all devices (i phone/ android browsers etc). I imagine it only needs a few tweaks. It would be for all the visual front end pages you see on the site (anything in the nav bar, and sub pages of the nav bar). I need this completed by Friday if possible.