How much swap did you have when this problem occured? I think too little swap is often the cause of problems with hibernation and suspend. I've heard that the automatic installer for Linux Mint will sometimes give you too little swap. For this reason, I usually manually partition my drive during installation. Swap should be twice the size of your RAM for hibernation and suspend to work well. My RAM is about 1GB, so I set swap to 2GB on a separate partition. However, you don't necessarily have to reinstall your system if you do have too little swap. The thing is, swap doesn't have to be on a separate partition - so you can create a swap file to your required size on an existing partition - there's info on this either here on the linux mint forum, or maybe on the ubuntu site.