Loss of storage on SSD following lock out

Problem getting Inspiron 2in1 5485 laptop to boot. Nothing until a combination of keys plus "On" button pressed.

System is linked to One Drive and previously showed a relatively modest measure of SSD drive space used.  Since lockout - re-open I have less than 25Gb available on 500GB drive.

Have trawled thru folders and finding odd things such as folder properties show 22.8 or 22.5 Gb, then I open and close folder and properties then show expected values - not 22.8GB. However, this does not change the available storage space on the SSD.

Any suggestions, please. Hair loss is getting to me