I set up a camapign to run both on search and content networks.
Set all 4 checkboxes and gave separate bids for search and content ads.
It is running well in search, but is not running at content - ZERO impressions.
The campaign started 36 hours ago.
What is the problem with content network? I know there are a lot of sites in my niche, so what can be the problem?
...The campaign started 36 hours ago...
This would probably put your start time on Saturday, which suggests the issue boils down to the ads not being reviewed/approved yet.
Ads must be reviewed and approved before they may be sent to either the search or content networks - and ads are approved on an extremely limited basis over the weekend.
The search impressions and clicks you are seeing are probably coming from Google.com, where the ads may run before they are reviewed/approved.
If you have the option, it is best to submit your new (or edited) ads mid-week rather than on Friday evening, or over the weekend, as this will likely result in a faster review.
AWA
If as AWA suggests it is Google policy to review all ads before they are shown then surely the sales pitch that Google uses saying "Your ads show up on Google almost instantly" is blatantly misleading.
I think you may have misunderstood my post rsndll. Bolding added below for clarification:
Ads must be reviewed and approved before they may be sent to either the search or content networks - and ads are approved on an extremely limited basis over the weekend.The search impressions and clicks you are seeing are probably coming from Google.com, where the ads may run before they are reviewed/approved
There are certainly exceptions to this rule, however, and your ads/keywords may fall into this category. If, for example, you are using keywords of a sensitive nature, your ads will need review/approval before running on Google.com. Sensitive keywords are not always obviously sensitive, BTW. As just one example, 'teen clothing' may not seem like a sensitive keyword - but on reflection I think you'll see that any keyword involving infants, toddlers, children, girls, boys, pre-teens, teens, etc will need review before ads may appear.
In any case, if you are curious as to why your keywords take several days to appear on Google.com, I'd advise contacting AdWords support - since they can see the account, they'll be able to give you specific information.
AWA
One thing: my ads are targeted toward XXX subject matter, it may be that those types of ads take longer.