Do you guys want me to post the <head> ? The css is being called in the head of the code. And what is weird is that the first time it will load it up fine but once you refresh the website will go to that text version.
No need to post your head at this stage - but can you just confirm the css is applied on the first load, but not on refresh. Plus, is this for every page (loads, then on refresh doesn't apply css), or for the whole site (loads for one page, then on every other page the css is not applied)?
Have you validated your css [jigsaw.w3.org]? I'd also validate your HTML just to be sure as well. There are many reasons the css may not be being applied consistently, but invalidities are one cause of erratic behaviour.
Also have you checked the schools filter/blocking rules, especially for the images?