If you are using a Power View Sheet and it is not rendering in the browser (see below screenshot):

You will want to verify if you are using Office Web Apps Server 2013 (WopiFrame.aspx) to render the workbook by examining the URL:

URL Example:

http://servername/sites/BICenter/_layouts/15/WopiFrame.aspx?sourcedoc=%2Fsites%2FBICenter%2FTest%20PowerPivot%20Gallery%2FPower%2Exlsx&action=view

If you are indeed using the WopiFrame.aspx, you will want to flip this (via the SharePoint 2013 Management Shell) to use the ExcelService.asmx via:

New-SPWOPISuppressionSetting -extension xlsx -action view

In the below article, you will see that Power View Sheets are not visible in Office Web Apps 2013 (WopiFrame.aspx):

Power View in Excel on Office 365 or in SharePoint Server
http://office.microsoft.com/en-us/excel-help/power-view-in-excel-on-office-365-or-in-sharepoint-server-HA103276078.aspx

Additional Information:

To verify the Suppression, run this command in the SharePoint 2013 Management Shell:

Get-SPWOPISuppressionSetting

It should return: XLSX VIEW

To remove this Suppression run this command in the SharePoint 2013 Management Shell:

Remove-SPWOPISuppressionSetting -extension xlsx -action view

To understand the above Office Web Apps SharePoint 2013 Management Shell Commands refer to the below article:

Windows PowerShell for Office Web Apps (SharePoint 2013)
http://technet.microsoft.com/en-us/library/jj219457(v=office.15).aspx