|Try opening in Safe mode:|
Click on the Start Button
In the Run Box enter:
You may need to use the complete path to Excel, which on my Win 7 64 bit is
C:\Program Files (x86)\Microsoft Office\Office12\Excel.exe
This forces Excel to start with no ADD-INS loaded, among other things.
If it opens faster, then you probably have a rogue ADD-IN,
just disable them all,
then one by one restart them until you hit the one that slows you down.