You are not using Oriental New Seagull Warmtone? Because that is the paper, which requires 3 minutes at F 5.6 at me setup for a 18*24 cm print. Compared to Ilford Multigrade or Kodak Polymax around 10 secs at F8.(posted 8809 days ago)How exhausted is your developer? Expose a bit of paper at 10 secs wide open lens. It should turn solid black pretty soon in the developer.
Did you change the lamp in the enlarger? Using a Kaiser 75 W instead of the required Philips 75W required 4 times more time.
You can check all three points by using a negative you have printed before succesfully, if it turns out o.k., than your latest negatives are too dense. If even this negative does not work then there is a mistake with your enlarger/developer system.
More info from you is required for a more detailed answer.
Kind regards
Wolfram