Unity 5.0 freezes on second launch.

I’ve tried reinstalling, but the problem persists.

Does it happen, if you try to open a project or just starting Unity?

If it happens at opening your project, try to create a new one and try to open it several times.
Maybe you have a weird bug in your project (maybe made with Unity 4.x?).

Other possibility: Your graphic card or display driver is corrupt. Or your whole OS is corrupt.