Phone loops on Samsung Galaxy s3 screen, cant get into recovery

Ok, this has been a nightmare.

Basically i installed a new custom rom, did everything right, and was working fine. Then i imported my contacts list off my ext sd card which was went weird. It basically hung on importing them in notifcations saying something like "such and such will be imported shortly" but didnt do anything, was stuck on the same person for ages. So i rebooted my phone. Well this is where it all came crashing down. Once it loaded back up it said something across the top of the screen that i struggled to read fast enough, but something like the sd card was being formatted and this couldnt be reversed, apps were missing, but the app logos were still on my home screens where i had placed them. However when i clicked on any downloaded and installed apps it said the app wasnt installed. I didnt even have google play in order to download anything. I could still use the internet so i searched for a google play app download and tried to install the .apk file. This didnt work, it simply crashed.

So i rebooted phone and now all it does is loop on the samsung galaxy s3 gt-i9300 screen. I cant turn the phone off (unless i take battery out) i cant get into cwm no matter how long i hold power, home and volume up keys. I can get into download mode, but wouldnt know what to do when in there, even with odin. trying to flash a stock rom to it fails every time.

Got no idea what to do.