Over 40.

This is assuming that you have your computer going, as switching it on, and Windows starting, is in fact starting a program.

Some of the below methods in later versions of Windows do not work but have usually been replaced by other methods.

Other than remotely controlling another computer I have not considered internet based programs as being Windows programs, otherwise there could be millions of way of starting programs.

Here is the List

1. - Double Clicking on a desktop Icon
2. - Press Enter on a selected item
3. - Right Clicking a program and selecting Open
4. - From All Programs
5. - From an item on the taskbar (Win7) or the quick launch bar (prior to Win 7)
6. - From recently used programs from the Start Menu
7. - By right clicking a program and selecting Run as Administrator
8. - Right clicking on a file and selecting Open With
9. - From the System Tray
10. - Typing the program name in Search Programs and files at the Bottom of the Start menu (Win 7)
11. - From the Run function in the Win XP start Menu
12. - By Clicking on a recently used file in the Win XP start menu
13. - By right clicking on a Program in the start menu that has a Jump List and clicking on it (Win 7)
14. - By right clicking a Program on the Task Bar and clicking on a Jump List item (Win 7)
15. - By holding down the Windows Key and pressing a number that represents the item in the task bar (Win 7)
16. - By holding down the Windows Key and pressing a letter (Eg. Win Key + E Starts Windows Explorer)
17. - Hold down the Windows Key and Press R and then enter a program name
18. - Hold down the Windows Key and Press O which opens the Ease or Access Centre and then select a program from it
19. - Hold down the Windows Key and Press X which opens the Windows Mobility Centre and then select one of its programs
20. - Press a hot key combination that has been set up in a shortcut to start a program
21. - From the Control Panel
22. - By double clicking a file in Windows Explorer
23. - By Dragging a file to a Short cut
24. - By typing the programs name from a DOS prompt
25. - From within a program that allows starting of other programs
26. - From within Windows Help and Support
27. - By running a Batch File (.bat)
28. - By placing a program in the Startup folder in the start menu (Starts when Windows Starts)
29. - By talking to the computer when Windows Speech Recognition is activated
30. - Via a program that starts programs at a predetermined date and time
31. - Via an event happening. eg's data changes, another program stops, a temperature is exceeded
32. - Via another computer that is networked to other computers
33. - By touching or clicking on a tile (Win 8)
34. - Via the Charm Bar (Win 8)
35. - For programs started from contextual menus swiping down from the top or up from the bottom of the screen (Win 8)
36. - From the Apps List (Win 8)
37. - From Recently Added in the Win 10 Start Menu
38. - From Setting in Win 10
39. - By double clicking on a recent file in the Win 10 File Explorer
40. - By showing the Jump list of a program on the start menu (Win 10) and the clicking a file in that list
41. - By right Clicking on start and then click on an item in the list
42. - From God Mode (a folder named GodMode.{ED7BA470-8E54-465E-825C-99712043E01C}) on the desktop (Win XP upwards)