Scanner not recognizing negatives

Hello everyone, my first time here, and in need of advice. I have an old Perfection 3200 which has always produced excellent scans from negs and slides. I kept my old computer as a spare, running Windows 7 so that I can continue using my scanner and photo printer (not compatible with Windows 10). However, after not using the scanner for a few weeks, I tried to scan some 35mm black and white negs. All I could get was a scan of the scanner bed and negs holder. And yes, I did remove the document mat. Everything was done as I’ve always done. I’ve tried everything I can think of - uninstalled and re-installed the scanner itself and the Epson software - and updated the drivers. But the result is always the same.
I will be grateful for all advice and suggestions, so thank you.
Posting screenshot of scans (hope it uploads OK)