A dashboard can read zero for a few reasons. Work through these in order.
1. Timezone mismatch (the most common cause)
Your dashboard reports in the Time zone set on your profile. If that doesn't match where you are, "today" may not have started yet. Set your correct local time zone under Edit Profile and the numbers will line up.
2. Date range
Widen the selected period, for example to Last 7 days. A card with no data in the chosen range shows zero even when the campaign is delivering fine.
3. The campaign genuinely isn't delivering
If the numbers are still zero over a wide range, it's not a reporting issue. Run Campaign Health Check on the campaign. It checks bid, budget, balance, creatives, targeting breadth and whether the Insertion Order has expired, and it usually names the cause in one step.
You don't have to catch this yourself. If a live campaign gets no impressions for 24 hours, we send a "not getting traffic" notice to your bell and by email, with the reason and the fix. See Notifications and email settings.
See also: Why isn't my campaign getting any traffic?
4. Conversions showing zero
If impressions and clicks look fine but Conversions reads zero, the postback usually isn't wired up. Check that your tracking URL carries {CLICK_ID} and that your tracker is firing back. See Supported Macros.
Conversions is one total across all your formats and channels. For Google campaigns, hover the number in the campaign list (or on the campaign page) to see Google's own "All conversions on Google" count.