Firstly, you need to check whether your account has a billing issue (payment declined or you reached threshold)If you don’t have any payment issue go further:
Please, check your ads and make sure they are not disapproved or paused. Watch this video tutorial to fix a disapproved ad. If your ads are enabled and eligible to show, for search campaigns use Ad Preview tool which helps to know why your ads don’t show up on search results.
For Display and Video campaigns you may have targeting restrictions or low bid issue. Learn more about solving these issues.
You can also use a Troubleshooter – Find out why you may not see your ad to find exact reason based on your case by providing additional details.
Shortly, check your payments, ad status, Preview your search ad (check Quality Score etc.), remove targeting restrictions, and try increasing your bids.
Helpful guide: Why you may not see your ad
Have a nice advertising!