my xbox 360 has stopped working all of a sudden

Does your power supply have a fuse on the plug?

Few years ago mine did same thing and was the fuse on the plug.

[...] my friend's DVD is stuck in there, and he want's it back. do you know what might have happend? [...]

You can follow the step in this page to manual open the tray and recover the disc: https://beta.support.xbox.com/help/xbox-360/console/manually-eject-disc

Since you say you have a "thick black Xbox", the instructions from napalm 31337's link won't help, as they are only for the S and E model of the Xbox 360, not your "thick" Xbox 360. 

In order to get a disc out of the original Xbox 360, you need to remove the faceplate. Instructions for the faceplate are here: https://support-origin.xbox.com/xbox-360/accessories/faceplate

The instructions on manually ejecting a disc from an original Xbox 360 console are here: https://support-origin.xbox.com/xbox-360/console/manually-eject-disc (you need to scroll to the very bottom of the page).

As for your power issue:

Please check the LED on the power supply brick. If the console is off, you should see an orange/amber light. With the console turned on, you should see a green light. 

If anything is broken, it should show a red light. 

Since you say you have a "thick black Xbox", the instructions from napalm 31337's link won't help, as they are only for the S and E model of the Xbox 360, not your "thick" Xbox 360. 

In order to get a disc out of the original Xbox 360, you need to remove the faceplate. Instructions for the faceplate are here: https://support-origin.xbox.com/xbox-360/accessories/faceplate

The instructions on manually ejecting a disc from an original Xbox 360 console are here: https://support-origin.xbox.com/xbox-360/console/manually-eject-disc (you need to scroll to the very bottom of the page).

As for your power issue:

Please check the LED on the power supply brick. If the console is off, you should see an orange/amber light. With the console turned on, you should see a green light. 

If anything is broken, it should show a red light. 

Since you say you have a "thick black Xbox", the instructions from napalm 31337's link won't help, as they are only for the S and E model of the Xbox 360, not your "thick" Xbox 360. 

In order to get a disc out of the original Xbox 360, you need to remove the faceplate. Instructions for the faceplate are here: https://support-origin.xbox.com/xbox-360/accessories/faceplate

The instructions on manually ejecting a disc from an original Xbox 360 console are here: https://support-origin.xbox.com/xbox-360/console/manually-eject-disc (you need to scroll to the very bottom of the page).

As for your power issue:

Please check the LED on the power supply brick. If the console is off, you should see an orange/amber light. With the console turned on, you should see a green light. 

If anything is broken, it should show a red light. 

here, i've taken a picture of it. looks like orange, but since i've never done this, i don't know exactly what it should look like!

here:

i don't know if it does. even if i did know, where would i get a replacement?

Unless you live in the United Kingdom, you probably don't have a fuse in the plug.