Polar 115ED Display Fault.

Hi,
We are presently having the display screen of our polar 115 ED,mach no 6531043 dark/blank and hence machines backguage and knife do not operate. This machine was recently acquired second hand and screen will sometimes come on with gullotine performing well and atimes after power up screen will be off and can come up again after switching off and on.Cutter will atimes just not work until knife is wound round manually.
I am positive with your assistance to troubleshoot this fault we will get good result.
Hope for a prompt response.
wunmi-50