Step1:Check searching the complete computer for XLSTART and than delete the contents.

1.Go to the location C:\Program File\Microsoft Office\Office 12\excel.exe
(if you are using a 64bit machine, then you would have to go to C:\Program files x86\Microsoft Office\Office 12\Excel.exe)
2.Right click on Excel.exe and click on Properties and then click on Compatibility tab. Check if you have any check mark in any of the compatibility mode options. Make sure you also click on the option "change settings for all users" tab at the bottom of the same screen and look for similar check boxes in the window.
3.Uncheck the option Run as Administrator option is you have it checked.
4.If you see any check boxes in the compatibility mode options, uncheck all the boxes and click on Apply and OK.
5.Try to open Excel now and check 

Step3: Search for excel.xlb, *.qat and *.pip. Try searching and renaming this files. Check if excel works.

If still it doesn't work than, go for contorl panel> programs> programs & features> highlight office 2007> change> click on drop down of excel and make it NOT AVAILABLE.

Open registry: start> run >regedit> ok
Take back and then delete the EXCEL FOLDERS
Browse to HKEY_CURRENT_USER\Software\Microsoft\Office
Browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office
Browse to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office

Start> control panel> programs> programs & features> highlight office 2007> change> click on drop down of excel and make it AVAILABLE.