On the HP LaserJet 1320, the attention light is a generic alarm. It can mean out of paper, paper jam, paper misfeed, cartridge missing, or cartridge door open. You can try cleaning the pickup roller or changing the separation pad. You can find these maintenance steps in the user manual starting on page 73 (page 83 of the PDF). HP has the manual here: http://h10032.www1.hp.com/ctg/Manual/c00208215
. More guides are available on the product page: https://support.hp.com/us-en/product/hp-laserjet-1320-printer-series/410622/model/410624/manuals
. Amazon has the separation pad available here: https://www.amazon.com/RM1-1298-HP-Separation-Tray-P2015/dp/B009SPB1H4
. Links to replacement pickup rollers are on this page. There are probably other sources for the parts as well.
Unfortunately, it can also indicate that a part has broken from paper pickup unit or the door closed sensor isn't working. At my home when our LaserJet 1320 reached ~10 years old, we got this message and decided to replace the printer. It wasn't worth trying to locate and repair the problem when cleaning the pickup roller and paper path didn't work.
I hope this helps.