It is possible to replace the LCD Backlight for your Janome MC 8000, take a look at this link below.
There are also included resources to do some other preliminary checks in a Self Test mode, to ensure that there are no other serious complications with your machine...also 'how to' access and replace LCD Backlight diagrams from the original MC 8000 Workshop Service and Repair Manual (Full Service and Repair Manual is also available separately):
https://www.bargainbox.com.au/product_info.php?products_id=1744&osCsid=d31625ce66f921412167a2f6edd9549f
Martyn
November 2009