There is an issue with MS Office Visio 2007 (and other versions it seems) where it has not been set up properly in the registry and it keeps attempting and failing to fix this every time it starts. It will work, but it is slow to start and as annoying as hell.
Running as Admin, reinstalling, attempting repair, etc, etc. will not correct this. There are any number of cheerful suggestions such as removing and re-installing, editing registry keys, etc. None of them worked until I found an incomplete list of registry keys requiring a fix and completed it. Fixing the keys below finally fixed it for me and it loads instantly now, finally.
It would appear that a default setting pointing to Visio Viewer rather than the Visio application proper is the issue.
The defective keys have this pattern:
.v?? (default)
VisioViewer.Viewer
application/vnd.ms-visio.viewer
They are found under HKEY_CLASSES_ROOT and the ones that needed alteration on my machine were as follows. Note that you should look for the VisioViewer value to make sure you have fixed them all.
Don't forget to set a restore point prior to editing the registry.
.vdx - (default)
Visio.Drawing.11
Content Type application/vnd.visio
.vsd - (default)
Visio.Drawing.11
Content Type application/vnd.visio
.vsl - (default)
Visio.AddOn.11
Content Type application/vnd.visio
.vss - (default)
Visio.Stencil.11
Content Type application/vnd.visio
.vst - (default)
Visio.Template.11
Content Type application/vnd.visio
.vsu - (default)
Visio.CustomUI.11
Content Type application/vnd.visio
.vsw - (default)
Visio.Workspace.11
Content Type application/vnd.visio
.vsx - (default)
Visio.Stencil.11
Content Type application/vnd.visio
.vtx - (default)
Visio.Template.11
Content Type application/vnd.visio