Default [Q] CMR boots, but main OS no longer boots

Hi, first of all I love this forum, this is my first time posting here but I found it indispensable when I was doing Android development-related stuff. However I've now managed to do some damage to my phone and need some expert advice!

So I was following the instructions on the CM wiki (I can't post external links yet but the address of the page is /w/Install_CM_for_i9100) for installing CM (I'm using a Mac). I got my phone into download mode and used Heimdall to flash ClockworkMod Recovery. This is where I think I went wrong: Heimdall found the phone fine and transferred everything, however the progress bar held at 'full' for about 5 minutes. After a while I thought it must be done and just doesn't have a confirmation once it's done, so I unplugged the phone and rebooted into ClockworkMod Recovery. Recovery boots up fine but when I try to connect using ADB the phone can't be found. When trying to boot up normally I now get the warning triangle below the Samsung Galaxy logo and the phone just turns off. Booting into download mode, Heimdall can no longer find the phone when it's connected. So, since I can't boot into my stock OS, and I can't transfer a new OS or re-flash CMR, does this mean my phone's bricked? Or is this a known issue with a fix? I've tried the search function on this board but can't find this exact issue.