NOTE: After you map a network drive to SharePoint Online, you must occasionally connect to the SharePoint Online site by using Internet Explorer and select the Stay signed in option. This prevents the session that's used by the mapped network drive from expiring. A mapped network drive that’s connected to SharePoint Online is only supported when these steps are performed within Internet Explorer.
If you previously didn’t check the Stay signed in option and then browse to a SharePoint Online site or the Office 365 portal and you're already signed in, you must first sign out, and then sign in again by using the Stay signed in option. To do this, follow these steps:
In the Office 365 ribbon, click the drop-down arrow next to your user name.
Click Sign out.
Close all browser windows.
Browse to the Office 365 portal.
Select the Stay signed in option, enter your Office 365 work or school account credentials, and then click Sign in (if it’s necessary).
Open a document library in Explorer View.
Try to access the mapped network drive.
Add your SharePoint Online sites to trusted sites
Make sure that the SharePoint Online URLs have been added to your Trusted sites zone in Internet Explorer. To do this, follow these steps:
Start Internet Explorer.
Depending on your version of Internet Explorer, take one of the following actions:
Click the Tools menu, and then click Internet options.
Click the gear icon, and then click Internet options.
Click the Security tab, click Trusted sites, and then click Sites.
In the Add this website to the zone box, type the URL for the SharePoint Online site that you want to add to the Trusted sites zone, and then click Add. For example, type https://contoso.sharepoint.com. (Here, the placeholder contoso represents the domain that you use for your organization.) Repeat this step for any additional sites that you want to add to this zone.
After you have added each site to the Websites list, click Close, and then click OK.
Check the status of the WebClient service
To keep the connection after you restart the computer, make sure that the WebClient service is running. (Be aware that the cookie will eventually time out.) To do this, follow these steps:
Follow the appropriate step for your operating system:
For Windows XP, Windows Vista, and Windows 7, click Start, click Run, type services.msc, and then press Enter.
For Windows 8, click Start, type services.msc, and then press Enter.
In the list of services, locate the WebClient service, and then make sure that its status in the Status column is set to Started. If it isn't set to Started, double-click the WebClientservice, click Start, and then click OK.
Make sure that the latest Windows updates are applied. If all the latest updates are applied, and the issue persists, make sure that the WebClient service is running.
NOTE: If the Startup Type for the WebClient service is set to Disabled, the map network drive functionality won't work correctly and you'll be unable to start the service. To enable the service, within the WebClient Properties dialog box, click the drop-down dialog for the Startup type: setting and then select either Manual or Automatic. The choice of Automatic is necessary for persistent drive mappings. After you complete this step, click Apply, click Start to start the service, and then click OK.