You should have to do a bit of troubleshootng by yourself. Apart from premiere whether your other programs and Windows in general are runnng flawlessly and whether there is any abrupt system shutdown? Whether 2 GB RAM is properly showing in your 'My Computer'? You should uninstall codecs one by one, try premiere and reinstall them. Actually you have to follow Trial And Error method. You may have to uninstall and reinstall premiere(never forget to save the project to a different location beforehand).

Anyway please let us know the result.