Have you checked that you have correctly installed the correct drivers for Hp Deskjet 3745?If yes then check all connections and if still it does not work then either your printer is faulty or try re installing your win 98.
How Will I Install Hp Deskjet 3745 To Windows 98?
You need relevant drivers to install your printer on Windows 98. You can download them from this link
h10025.www1.hp.com
h10025.www1.hp.com