It's worth checking it's not in a strange mode, as Tonto suggested. (No live view on a D40!)
I've got a D40 which must be around 5 years old with well over 13,000 shutter actuations, and it runs fine.
Dammit - i read the original post as a 40D instead of D40. Oops
Is it definately sticking ?
Its not in delay mode or anything , or live view ? They may be a silly questions, but i dont know your level of expertise
Common fault i'm afraid Natalie
Several fixes mentioned include a diy take apart and repair, all details here http://www.youtube.com/watch?v=CAWGScQeC5g
Others have squirted switch contact cleaner down the shutter button which may work
The problem comes from crud getting between the contacts, Canon at Elstree would no doubt charge the standard rate at about 150 quid
Cheers
Rich
Isopropyl alcohol worked for me on one of my photobuddies 40D.
Roughly along the lines of pouring into the battery compartment and draining out the shutter button while activating the shutter.
The grot that is trapped under the shutter button is shifted.
You can buy the fluid on eBay; took me only two attempts at this to get the shutter working properly and there were no side effects.
Read and understand what you need to do (Google and YouTube) before attempting!
Here's a good link to show what I mean
http://www.youtube.com/watch?v=tB_gSqyidI0
there is the very old trick of hanging items that stick over a dish of meths which then let the fumes free sticky things. best left overnight to work. Worth a try.
Realspeed