Thanks for your answers. I added my specs but I will sum them here too
AMD X2 4800+ EE (but I also had a 4600+)
Asus M2N-SLi Deluxe with latest f/w
OCZ 2 *1GB + 2*512MB. (This model
Sapphire ATi X1950 Pro PCIE 512MB
1 * Seagate 80GB for System and Programs + 1 * Seagate 120GB for Video stuff. Both are SATA 2 but in the past I had WD Sata 1 HDDs with the same capacity.
Windows Vista Ultimate SP1 with all the updates (but problem existed with Windows Vista Ultimate pre SP1).
AverMedia DVD EZMaker Gold PCI. I had it to the last PCI slot on the bottom of the mobo but I also moved it one slot up to check.
I suppose this is what matters and I won't add my PSU or DVDR drives.
I have latest reference drivers for everything aka from AMD-ATi site, nVidia (for my motherboard), Asus (for audio), AverMedia (for capture card).
The only codec I have installed is Keopi's latest XviD release. In the past I also had the original DivX codec.
For A/V I had NOD32 (but expired) and now I bought Avira Antivir Premium.
I know, I mentioned nearly everything but if you require any further help, please let me know.
Thanks for all your help.