Hikvision DS-7204HGHI-SH no longer records

It worked fine since around last December, recording only on motion activation. Then last month I started using the iVMS-4200 software instead of the buggy browser interface. I noticed that it was no longer recording. Turns out the disk had filled up and it was ignoring the 'Overwrite old recordings' setting. So I formatted the hard drive to dump the old recordings. It now send the emails every time there is a motion activation but no images are attached and no recordings ever appear on the device. There is 800GB free on the drive.

Even when I start recording manually, no recording files can be found. Even instant playback fails with 'No record file found'.

What can I do?? I have stepped through every setting looking for something I missed....