How to Lock a site collection manually

1. Browse to SharePoint Central Administration.

2. On the Central Administration page, under Application Management, click Configure quotas and locks.

3. On the Site Collection Quotas and Locks page, select the site collection where you want to place a lock

4. In the Site Lock Information section, select Adding content prevented or No access.

5. If you lock a site collection with Adding content prevented or No access, you must type an explanation in the Additional lock information box.

6. Click OK.