yes, this is RAM problem but it can easily resolve just upgrade your computer memory

I think 512MB RAM is not enough to run Windows Vista smoothly. I would like to recommend you press F8 when restart and enter safe mode for debugging purposes.

Hello
Many PC manufacturers pack their new computers with programs you didn’t order and might not want. These often include trial editions and limited edition versions of programs that software companies hope you will try, find useful, and then pay to upgrade to full versions or newer versions. If you decide you don’t want them, keeping the software on your computer might slow it down by using precious memory, disk space, and processing power.
It’s a good idea to uninstall all the programs you don’t plan to use. This should include both manufacturer-installed software and software you installed yourself but don’t want anymore—especially utility programs designed to help manage and tune your computer’s hardware and software. Utility programs such as virus scanners, disk cleaners, and backup tools often run automatically at start up, quietly chugging along in the background where you can’t see them. Many people have no idea they are even running.
Even if your PC is older, it might contain manufacturer-installed programs that you never noticed or have since forgotten about. It’s never too late to remove these and get rid of the clutter and wasted system resources. Maybe you thought you might use the software someday, but never did. Uninstall it and see if your PC runs faster.

I find Vista is just about OK with 1Gb RAM but will slow once a few browser sessions or other apps are open at the same time. 2Gb is the minimum for a half decent performing Vista system.

Yeah,512MB RAM is not enough to run vista,you have to at least 1GB RAM.