4 GB RAM is usable, if marginal. 8+ would be better as video editing is resource intensive.
One thing you might do prior to beginning a new project is click OPTIONS|DISK tab and Clear Unused Cache Files. Loading will be slow at first, but once the clips are cached a reload will be faster.
Share your project, as detailed above, and someone will check out how it exports. You might also consider upgrading to the latest Windows version.
For licensed users upgrades are free for up to six months from purchase. After that, VP will continue to fully function but a fee will be required in order to register the newest.