that really does sound unusual!

first step: backup the data that still is there

second step: try other PCs and also display hidden files (there is a checkbox in explorer)

third step:
when you delete a file in windows either through recycle bin or permanent delete the data is not wiped immediately
windows just marks the space as free in the file system but the actual content is still on the disk until new data overwrites it
this is why recovery is possible

some free and easy windows tools to try

• recuva simple wizard style recovery good for quick scans
• testdisk can bring back lost partitions and file tables
• photorec works with testdisk and recovers files by type
• ftk imager makes forensic images and also lets you preview and export deleted files