Dell Dimension XPS T500

Today I acquired the above computer at a surplus auction for $5.00.
Could anyone tell me how to open the case on the Dell T500??!! Please!!
I am at a complete loss, don’t want to break anything, and it’s not the first computer I opened up 🙁
There are no visible screws, except one big one in the back, but loosening it doesn’t help. Cannot pop off the front panel either.

Thanks in advance.
rue gamer