It's an old Dell optiplex 380 (Core 2 Duo E7500)
System is on a Kingston SSD (A400 ) I added about a year ago, data is on another HD.
Three months ago I had an error probably at boot time (black screen with error message, maybe after a reboot following Windows update), Chkdsk ran and found errors.
I reran chkdsk /f more recently, no errors found (I didn't do a chkdsk /r though)