all password reset links are going to the error 404 page, please what could be the issue

Go to Settings > Permalinks and re-save oermslinks to refresh saved structure.
Try again.

If does not help, review each oaram and ideally use original one.

I haven't been able to verify any account despite re-saving it as you suggested. The email verification and account validation processes are still not working properly and are still showing error 404, OOPS! Page Not Found!

Please all my newly registered users not been able to validate there account and cannot post new ads, please help me

If you resaved, then all looks good from Osclass point of view.
Check if your activate urls match this format