The way you use the `[pageBlockTable][1]` is little confusing as I see. You have to add `apex:column` tag in order to bring the columns of the table. Try below code for the table. This way you can add more columns to your table.


    <apex:pageBlockTable id="sampleGrid" value="{!Contact.AccountId}" var="a">
    	<apex:column >
    		<apex:facet name="header">Account</apex:facet>
    		<apex:inputfield label="Account"  value="{!Contact.AccountId}" />
    	</apex:column>
    </apex:pageBlockTable>


  [1]: https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_compref_pageBlockTable.htm