Leaving aside the kinds of deliberate FREEZE that Raudona mentioned in #7, if I wanted to use the verb freeze in connection with the display on a computer screen not changing for some period of time when it actually should, I would say the display has [just] frozen or the display is frozen. I have never come across anyone using freezed (prior to reading the OP of this thread). I'd talk about the display being frozen, not the screen, since the screen/monitor is usually still doing its thing correctly in that it continues to render the input signal from the computer into an image sixty (or whatever) times a second - it's the signal from the computer that represents the display that is not changing.
Also, rather than talking about freezing, I'd distinguish between things hanging up and things crashing. If processes (programs) are hung [up], then they're still running, but doing so in a way (e.g. running in a tight loop) such that they're no longer accepting input or producing output. If processes crash, they die, possibly producing diagnostic output, and are no longer running. If your whole computer has hung up, it's still running, but again doing so in a way such that it's no longer accepting input or producing output (the display is frozen), but for example the mouse pointer amy still move, the Caps Lock light can be toggled on and off, and there may still be hard disk and/or network activity. If it's crashed, on the other hand, there will be none of these Lebenszeichen, and again there may be diagnostic output (e.g. BSOD - Blue Screen Of Death), or it may even reset.
Bildschirme selten telefonieren - Nowadays not, but I suspect the use of hung up in connection with 'frozen' computers comes originally from the days of terminals connecting to mainframes via telephone modems. It was presumably quite common for one end or the other to hang up at inopportune moments.