The latest version is here. Try it out. An eventual upgrade isn't free though, because it's been several years since you purchased.
Video editing is resource intensive; what are the specs for your PC - CPU, GPU, RAM, available disk space, etc. ?
Lowering preview resolution may help. Right-click in the preview window to set it.
To eliminate the possibility there is cache corruption, "clear unused files." That button should be under an OPTION tab.