a lot of hidden space on harddrive

Hi! I have a question which Might or might not has something to do with avast?
I have 3 computers with windows 7 and avast internet security. This spring I had a problem with avast on one of them and I was adviced to cleanup with different Tools and uninstall parts of windows security. After this 2 of my computers work ok but one of them, my lenovo laptop became slower. I have been cleaning it and done different things after this to no avail. Now when I want to update it to windows 10 I investigated my harddrive after removing a lot of stuff and a few programs. This is something i should have done when the computer slowed down but overlooked since it is obvous but maybe too obvious.
My harddrive seems almost full with 180 gb occupied space and I can only account for around 60 gb. After a whole day of doing all i can to remove material and find what is there the situation is the same and I can find no way to see what is hidden. I even used a stick with ubuntu to check since Linux programs sometimes can find what windows cannot.
Since this problem seems to have arrised? when I followed advice from this forum I thought that maybe someone could help and even if it is not an advast problem maybe someone can give advice and/or tell me of a program which might find the hidden stuff which must be at least 120GB.
Regards POSweden

Best Regards PO Sylwan