Browsers no longer displaying icons in dashboard

All of a sudden my computer stopped displaying the proper icons in the dashboard. For example a work item viewlet displaying a table with all work item status "in progress", "closed" etc is displaying the same icon for everything. This includes custom enumerations/icons, priority and severity icons.

I can see the proper icons in the work item view and the plan view. Also my colleagues can see the proper icons in all views. Does anyone know how to fix this?