Cannot access IMac OS (2009 X Snow Leopard) from Window 7 Bootcamp Control Panel or option key

I'm currently using an Imac 2009 running (Mac OS X Snow Leopard 10.6.6) and I wish to switch from my Windows 7 to my Mac OS and make that the default OS. Using the option key does not work. Bootcamp control panel can't find it either. It seems I'm unable to get back into Mac and this didn't seem to be an issues a year or ago? It appears that my Mac HD still exists here, and I still have the install disk and often back up my files using time machine. What would be the best solution for this, is there away to get back into my Mac or will I have to reinstall and back up from time machine (Unfortunately I know longer have the Windows 7 install disc) thank you in advanced. NB I did look at the below link but wasn't sure if it was relevant to my issue as I'm essentially locked out of my Mac OS. https://apple.stackexchange.com/questions/310109/boot-camp-control-panel-macos-partition-doesnt-show-up/418573