3d aps and video conversion causing freezing

[mrnuke]

On my computer lately while trying to play games, every time the computer went into 3d, it'd freeze up almost 30 seconds into it loading a 3d world. Also while converting video files to dvd friendly files it freezes at well. Now at first i thought it was a graphics card issue, but after getting a new card today and reinstalling all the new drivers, its still doing the same thing. I've run memtest86+ and the RAM has no errors. I have a 700w OCZ gamestream ps, AMD 3500+ newcastle, DFI NF4 SLI-DR, new ATI 3870 and a 320gb WD HD. The only other thing i can think of would be the HD, but i'd like your input. Thanks in advance.