Links not working on Multisite

I have a main WordPress installation http://www.ypant.co.uk.

My network admin has enabled wildcard DNS so that now I have multisites
E.g. art.ypant.co.uk and maths.ypant.co.uk (this is a school)

However whilst the main URL for each site works and I can access the dashboard for each site without problems, the links on these sites don’t work.

I need to try and resolve this urgently as I have 20 teachers coming in on Thursday to set up their own sites. They are all set up but it doesn’t look good if there’s only a home page!

I am using twentyten (newest edition) for all subsites but have not upgraded WordPress as it caused my main site to crash when I did and I see there are some problems with it. I don’t currently have time to investigate.