All the proxies you try should be blocked by your school. That is because most schools use content blocking software. It blocks new proxies 98% of the time because of their content (that they are a proxy), not because of the web address.
You really should be careful using a proxy at school. Is it worth risking getting into trouble?
1. School computer admin take security seriously, they have to, it's a main part of their job.
2. Proxies posted here normally contain spyware/malware and viruses, they also track what you type, so they can get access to your mail, myspace, facebook accounts etc to send spam from them. Do you think people set these proxies sites up for free? They are getting something out of you using them and it's 99% criminal.
3. Because of the danger from using a proxy, computer admin block them well, although it's always a cat and mouse game. So it's unlikely you will even get through on one for long anyway. Also they can trace in the logs that you went to a proxy site.
4. If you do use one and the computer system gets infected with a virus, you will be in a lot of trouble, losing computer rights and possible suspension. Also, many students have had to pay for the repair work. Having your parents get a bill for you messing around will go down well won't it?
So please consider this a friendly warning. Is it really worth it? Can't you just wait to use myspace etc at home or in a public library?