If you want to just level the bed I recommend doing that manually, if there are no other ways.
I’ve got a *generic brand name* DIY Prusa i3 too, and I’ve never had the luxury of Auto-Bed-Leveling, but the thing still works fine.
All you need to do is move the head up and down a little when the printer is off (by turning the Z-Axis-Motors synchronously), and then, by looking or a piece of paper, try to adjust the nozzle height as far down as possible without having it touch the bed.
If that isn’t the problem, and instead the Axes are moving in the wrong dimensions, I recommend RepRap Calculator - Original Prusa 3D Printers to figure out some good Steps/MM values for the different pulleys or threaded rods the printer is using.
Honestly though, if you google around a bit and spend some time with that stuff it really isn’t all that hard to calibrate the printer properly ^^
-- Sidenote –
If you want to simply move the nozzle up or down a bit, you can Pronterface or similar control software to send raw G-Code commands.
Then use the following to move the nozzle up or down:
G91 ; Relative Movements
G1 Z1 ; For upwards movement of one millimeter
G1 Z-1; For downwards movement
And don’t forget G90 again for absolute positioning afterwards!!
You can then, once finished positioning your nozzle, set the current printer position with
G92 Z0