help with avrdude: stk500_getsync(): not in sync: resp=0x30 uno

I've been using my arduino uno for the past 3 months and haven't had any issues uploading code before. When i most recently tried to upload a sketch though I got the error avrdude: stk500_getsync(): not in sync: resp=0x30. I've updated my arduino IDE to the most recent version (1.0.5) and tried again. Same problem. I've tried doing this in both ubuntu and windows 7 and have checked m com ports on windows. When i upload the TX and RX lights still flash as the software uploads but then i get the error. I've also noticed that when i reset my board it doesn't revert to blinking pin 13 but instead my previous sketch (blinking twelve and thirteen). I'm not sure if this has anything to do with the problem. I believe that my drivers are properly installed although I haven't done anything other than installing the IDE in ubuntu. Thanks in advance for your help.

I've also noticed that when i reset my board it doesn't revert to blinking pin 13

It sounds to me that the bootloader may have to be reloaded.