KR 4500, unresponsive, screen blank and lit

I've just brought this piano home after purchasing it from a lady who loved it dearly but could find no one to service it for her. My intention is to service it myself and when running properly, return it to this wonderful lady, along with a full refund. Any ideas out there? When unit is plugged in and powered up things look normal. Orange light on floppy is on. Screen lit green but blank. Red power light at front is lit. I'll put whatever cash it takes into this. Need some direction for starters. I'd appreciate any reply. Thanks. Tony.V. St. Catharines, Ontario, Canada.