3Gb is the max for a 32bit OS so it’s probably not that. There are a number of things to check but, most importantly, try to determine if it’s the computer, the software or the video files. For instance, bad RAM can produce render errors, or a system that goes into sleep mode, or a hard drive with too many errors or too little room to render. Software: if you are using a lite version or program and doing a CPU intensive project, the program may not be able to handle the length or number of video effects. Also, video files can get corrupted, your source files may be corrupted already. In that case you will have to rebuild your assets and check them to make sure thay all play through.