Lots of Access Denied errors

Hello.

I am using SharePoint 2010 Standard and get Access Denied boxes when trying to access a variety of pages, despite being a Site Collection Administrator and a Farm Administrator.   I also have Full Control to all levels of the site.

The pages I cannot access include:

• http://intranet/_Layouts/areacachesettings.aspx
• http://intranet/_Layouts/sitemanager.aspx?Source={WebUrl}_layouts/settings.aspx
• http://intranet/_Layouts/SiteManager.aspx?lro=all
• http://intranet/_Layouts/TranslatableSettings.aspx

Additionally, I get Access Denied when I try to:

• check permissions on document libraries, folders and individual files, yet I can check permissions at the site level
• create a workflow

I have checked the USL log and see this entry, but it isn't much help:

"Unknown SPRequest error occurred. More information: 0x80070005"

Any suggestions on how to troubleshoot or resolve this would be gratefully received.