My disk has 146GB of space, and the only folder is 74.9 GB, but the free space is only 34 MB. What happened?

You probably have system files and protected operating system files hidden.

You can show hidden files by opening a file explorer window then press ALT and the menu bar should appear. On the menu bar, click tools, then folder options. Click on the view tab and choose show hidden files and folders. Then remove the check from hide protected operating system files.

Click OK to close the folder options windows I believe the menu bar disappears after you exit the tools menu, but if it stays, you can press alt to get it off your screen.

Now you should be able to see what is using up so much space. Typically, your pagefile.sys and hiberfil.sys will each be using a chunk of hard drive space equal to your RAM. If you have 8gb RAM, that's 16gb hard drive space dedicated to them. Temp files and the C:\Windows\WINSXS folder also tend to grow pretty large if you don't ever clean them up.

operating sytem needs taking into account too. Admin tools, clean drive, C, now select system, delete old windows installations and shadow copies to gain space, defrag it too be good

its the operating system and stuff i think you should upgrade to a bigger hard drive or ssd if you have a desktop you dont need to get rid of the hard drive/ssd you can just add the hard drive/ssd

You may be looking at backup information or an alternate partition.

start a dosbox do a dir/s and see where it all goes.

programs?