Well, at first the different ISP was the only difference I could see. Then it started on the school's internet as well, which comes from a different ISP. Also, the problem started at the exact same time the ISP had a hardware failure a few weeks ago. I honestly don't know much about PHP, but I can't think of anything the ISP would have done that would have affected PHP pages only. I've talked to them, and they said everything should be normal now and that it was something on my end, not their end. (Of course, they always say that, don't they?)
As to how or why the problem was created... well, usually when my internet gets hosed for speed, PHP and XML pages start loading as text only. Like I said, normally this stops when my ISP replaces the gerbil that powers their server. But this time, the problem hasn't entirely fixed itself. I'm trying to find out at what level the failure occurred and who I should be talking to.
See, internet in Thailand is all controlled by CAT (Communications Authority of Thailand), if they have a failure in their equipment, everyone suffers. It goes CAT -> ISPs -> end users. ISPs are not allowed a direct line out, makes it easier for the government censor... er, I mean monitor the internet. Anyway, if it was a hardware failure at CAT, that might explain why I started having problems at school as well. To find out where the problem occurred might be difficult though. They don't always know, or willingly give out, that information.
At home, the desktop is wired directly to the router and the laptop uses wireless. At the school, the laptop is wired in the router in their library or, at times, connected wireless to a different router (not the one in the library).
I'm also going to take a look from my girlfriend's laptop tonight. She's finally back from home after Chinese New Year, so I can have access to her machine and see how if it works out or not.
