A Class 6 memory card is required for recording HD quality video. Not sure if yours is HD or not. Anything lower than Class 6 (such as Class 4 or Class 2) will result in recording issues and possibly skipping some video here & there.
As for the 30 seconds of filming limit...
1) It may be the memory card...that is if it's lower than Class 6. As a rule of thumb, when it doubt, buy Class 6 or better. Class 10 is the next step up, but it's a quite a bit more expensive.
2) Make sure you are using good, Lithium batteries...not Alkaline. Alkaline batteries will shut the camera down after a very short period.
Here are more tips on shortened recordings from GoPro's Website, followed by their Support Contact Info:
The batteries do not last very long.
- It is not recommended that you use Alkaline batteries. Lithium batteries have the best results and longest battery life. Rechargeable NiMH are another option in mild weather.
- Is it cold out? Battery life can definitely be affected by the cold! Please make sure you only use Energizer Lithium batteries in the cold, as any other battery type will perform poorly. In cold temps, you can expect about half of the normal run time when using the Energizer Lithium batteries.
- Still having shortened records with a good set of the recommended batteries? Please email our support team through http://gopro.com/support for further assistance.