iphone personal hotspot not working on ipad or laptops, flashing on and off

Hi,

I hope someone can help.

I have an iphone 4, running iOS 5.1 and its been working fine until tonight. I use the personal hotspot on it, to share my internet connection (3G) to my ipad3. All has been fine, but tonight, when I try and connect to my iphone hotspot, the ipad tries to connect, shows up then disconnects, then shows up and disconnects again, does this maybe 4-5 times then stops and ipad don't try again until I tap it. On the iphone, it shows the blue banner at top saying 1 connection, and this goes on and off at the same time, but then sits on 1 connection, even though the ipad hasn't got a connection.

So I deleted the connection on my ipad and readded it, just the same. tried changed the name of my iphone and also the password, still the same. rebooted iphone and ipad, still the same. I then tried connecting my netbook and my laptop to it, it will sometimes get a connection to the iPhone but then come up limited connection and not allow internet access. I got it connected to my ipad3 for about 10 mins, then it dropped the connection, and won't reconnect again.

I really don't know why this has started happening. The wifi on the phone seems ok, as can connect to my router when at home fine.

Anyone any ideas? Don't really want to restore it etc

Thanks

Paul