Electrical problem? both the stitch indicator light and needle up/down button are not working after having it serviced for a mechanical problem. What could cause this?

Your machine looks quite similar to some of the older Berninas I've worked on in the past. Perhaps your machine has seized due to the old oil solidifying. This could have happened with the reverse mechanism and the selector levers/buttons on your machine.

Wheel on right side that controls the needle up and down is very tight...

the stitch length is governed by the cam action connected to the walking foot
that means that the stitch length is governed by the amount of material that is pulled through in the period of time that the needle comes up and goes down
normally the cam action is set by the stitch length lever/ reverse lever
if there is a necessity for a longer stitch, the cam would have to be changed on the drive shaft underneath
That will require a discussion with a sewing machine mechanic to determine if there are cams or other linkages that can be fitted to alter the stitch length for the manufactured maximum

could be the computer is not working right or could be a mechanical problem, if the problem doesn't stop the machine needs to be checked

E7 means
The start/stop button, reverse/reinforcement stitch button
or the thread cutter button was pressed while no thread
cassette was installed. If the start/stop button is pressed before the sewing machine is correctly set up or if an operation is performed
incorrectly, an error message appears in the stitch indicator. Follow the instructions that appear.
If you press (Stitch selection key) or do the operation correctly while the error message is displayed, the
message disappears

sure, put on the buttonhole foot after putting a button into it and using the screw knob to set the length you want.
Turn stitch length knob and stitch width knobs to zero, (always set them to zero first to avoid wear on the stitch selection mechanisim) then turn the left stitch selector knob to the blue button hole symbol. Now turn middle knob stitch width, to the blue buttonhole symbol. Now turn right knob stitch length to blue 1, sew down the first side of your buttonhole until foot slide in the buttonhole foot reaches end stop. raise needle and turn stitch length to blue 2, and sew three bar tacks across buttonhole. Again, raise needle and then turn stitch length to blue 3 and sew back down otherside of buttonhole until you reach the end stop. Needle up, turn length know to blue 4 and sew three bartacks to end. there is a last blue symbol dot on stitch length knob, this will sew a stitch in place to tie off the ends. Raise pressure foot, remove your work and draw top threads to underside with a needle, and tie off or use a dot of fray stop. Done! if you don't have a manual you could email me and I'll send you a copy of mine, tallygirl98 at yahoo dot com.

The switch could be bad or the mechanics that physically move the needle for the zig zag could be broken/worn. Hope you get it fixed soon!

If the needle wont go up and down at all when you turn the handwheel, it's most likely due to fluff and general muck has got into the basting stitch mechanism - this is a frequent failure on Artista models that have the basting stitch option. Try gently pushing the needle bar up at the same time as turning the handwheel ... with any luck the basting solenoid clutch will re-engage with the hole in the needle bar. If this works, it's only a temporary fix and tells you that your machine is overdue for a service !!!! Getting the gunge out of the basting mechanism needs to be done by a Bernina service agent. Trouble is, some embroidery patterns use the basting mechanism to raise the needle-bar out of the way whilst the hoop moves to a distant point on the embroidery, so if you 'fix it' using the above method, it may well fail again when you try to do another embroidery. Sorry !

Check your bobbin spindle. If engaged (pushed toward the right) LED will not light. When the clutch knob is pulled out, when you wind a bobbin, the up & down needle will not move. So you must push the clutch knob in again to let the up & down needle go up and down. The clutch knob on my machine is in the large hand wheel upper right side of my machine.

Hi there, don't know your machine but you can do a plaiin buttonhole manually.
Set machine up for zigzag stitch, needle to left side, mark out the size you need with pins or marker pen. Start at the top and set for widest zigzag with 0 length for the top bar, cannot give sizes as don't know the button you are using, about 6 stitches, set stitch width to just over half the width of top bar and length to approx 0.5. Stitch down to bottom marker and again set up ffor the wide bar, do the same amount of stitches as the top, finish with needle down at the outside edge, turn work so that you will now stitch down the other side to meet the top bar, not forgetting to adjust stitch length and width again.
Hope this helps
Ellie

Mechanical.

Here is an overview - http://www.oksewingandvacuum.com/3007.htm