My Sim card or Phone isn't working properly, HELP?

I am using a LG Optimus gt540, on the Vodaphone network and it keeps saying no service, i have take out he sim numerous times, run the phone dead, it has happened before but usually i turn the phone off and take ot the sim then re-insert it and it works again but now it just won't work, i have been on the Vodaphone site and it says that there is network upgrades for QLD but the dates that are on the site have gone past, the etwork was working for me, for about an hour but then stoppped again and now won't work.