Matz45 - You're using Win-XP, I think. For best results with current versions of programs like VLC, etc, if you haven't updated to Service Pack 3 yet, that might improve matters. SP3 is a free download from Microsoft - 316MB, and quite easy to do, though it can take a while - just follow the prompts and instructions. If unsure there are also Guides online.
If you are already on XP-Pro SP3, and having problems running programs, you might run your Antivirus program, and ensure that the "all files" option is selected.
Uninstall progams that you're having trouble with - such as VLC - before running the full in-depth AV check.
After that check, download the latest version of VLC for Windows - and before double-clicking the *.exe to install it - check that download with your Antivirus program!
Re "whether Avidemux works or not" - while it might be a bit "plain" to look at when first installed, it actually has a lot of functions, including format conversion, size conversion, audio resampling and conversion, filters (Colour, Sharpen, Denoise, and more), framerate per second altering, and a lot more - all with "Preview" so you can see what changes will do, before you do them.
It will also do basic editing, trimming, add fades start-finish of clips, append (join) clips, and extract and save audio (you can extract/save audio from camera clips, then delete the audio from the video, and add the audio back later in a larger editor as suits better.)
You can also use Avidemux to extract/save audio - say, AAC, AC3, etc, from videos or movies (check the legality of doing that with downloads or commercial products, in your region) - to play in audio devices.
You can install and use the free Audacity for Windows as a quite good basic to medium level audio-editor, to convert formats, edit audio clips, clean-up "noise" from tracks, apply effects, echo and more,etc. Audacity is very good for preparing audio extracted from camera clips for use in a video-editor.
You mention Sony's Playstation (my mid-teens godson also has that) - so Avidemux's ability to create Playstation compatible *.mp4 videos might interest you.
Prepare the video first - you can use Avidemux for that - then open it in Avidemux. Go to the menu-bar, click Auto - then Sony Playstation Portable. A small box will open. The top field - click the arrow-tab at the right end. A list will drop, offering sizes to suit your model of Playstation - 480 x 272, 720 x 480, etc (obviously, it can't be bigger than the video you're converting from...) - so select that.
Unless you're intending to change the Aspect Ratio, leave Source and Destination fields at 1:1. Click OK, and a window will open for you to browse or click to the desired output destination. Select that and click OK. Your Playstation compatible video will arrive there with *.mp4 file extension.
Any questions on the above - post back, and we can work through it.