Problem, cant get desktop to appear

My aunt has a OPTIPlex 270 I believe, recently it froze while printing, and I had her unplug it to shut off. When turn on  it seems you see the name Dell an model number an the bar graph fill, but dont get a desktop, but do hear  for a few seconds a high pitch ringing out of top of tower.  I then took this to a technition, but it worked fine for him. I brought it home an still works same, I did buy a new monitor, no difference. I unhooked tower an took to my residence and tried tower, windows starts as normal when used . Once again I took back to my aunt's an still windows does not appear when hooked up at her place. Seems to act up only at owners location? I used a simply electrical meter  to check household electrical current, it said it was 118 volts.  Help, jrhxxxx