I can't play files I used to be able to play

Last night I tried playing some .mkv and .ogm files, which had worked just fine before. I have the combined community codec and then for good measures I installed Matroska while attempting to fix the problem. I only started experiencing these problems after I got hooked up to the internet. Whether it’s my viruscan program... or azureus or something else I don’t know. The error states:

E:\Azumanga Daioh - 01.mkv::Video

Media Type 0:
--------------------------
Video: DivX 5 640x480 23.98fps

AM_MEDIA_TYPE:
majortype: MEDIATYPE_Video {73646976-0000-0010-8000-00AA00389B71}
subtype: Unknown GUID Name {30355844-0000-0010-8000-00AA00389B71}
formattype: FORMAT_VideoInfo2 {F72A76A0-EB0A-11D0-ACE4-0000C0CC16BA}
bFixedSizeSamples: 0
bTemporalCompression: 0
lSampleSize: 1
cbFormat: 112

VIDEOINFOHEADER:
rcSource: (0,0)-(0,0)
rcTarget: (0,0)-(0,0)
dwBitRate: 0
dwBitErrorRate: 0
AvgTimePerFrame: 417083

VIDEOINFOHEADER2:
dwInterlaceFlags: 0x00000000
dwCopyProtectFlags: 0x00000000
dwPictAspectRatioX: 640
dwPictAspectRatioY: 480
dwControlFlags: 0x00000000
dwReserved2: 0x00000000

BITMAPINFOHEADER:
biSize: 40
biWidth: 640
biHeight: 480
biPlanes: 1
biBitCount: 24
biCompression: DX50
biSizeImage: 1843200
biXPelsPerMeter: 0
biYPelsPerMeter: 0
biYPelsPerMeter: 0
biClrUsed: 0
biClrImportant: 0

pbFormat:
0000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0020: 00 00 00 00 00 00 00 00 3b 5d 06 00 00 00 00 00 ........;]......
0030: 00 00 00 00 00 00 00 00 80 02 00 00 e0 01 00 00 ........€...à...
0040: 00 00 00 00 00 00 00 00 28 00 00 00 80 02 00 00 ........(...€...
0050: e0 01 00 00 01 00 18 00 44 58 35 30 00 20 1c 00 à.......DX50. ..
0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................


Media Type 1:
--------------------------
Video: DivX 5 640x480 23.98fps

AM_MEDIA_TYPE:
majortype: MEDIATYPE_Video {73646976-0000-0010-8000-00AA00389B71}
subtype: Unknown GUID Name {30355844-0000-0010-8000-00AA00389B71}
formattype: FORMAT_VideoInfo {05589F80-C356-11CE-BF01-00AA0055595A}
bFixedSizeSamples: 0
bTemporalCompression: 0
lSampleSize: 1
cbFormat: 88

VIDEOINFOHEADER:
rcSource: (0,0)-(0,0)
rcTarget: (0,0)-(0,0)
dwBitRate: 0
dwBitErrorRate: 0
AvgTimePerFrame: 417083

BITMAPINFOHEADER:
biSize: 40
biWidth: 640
biHeight: 480
biPlanes: 1
biBitCount: 24
biCompression: DX50
biSizeImage: 1843200
biXPelsPerMeter: 0
biYPelsPerMeter: 0
biYPelsPerMeter: 0
biClrUsed: 0
biClrImportant: 0

pbFormat:
0000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0020: 00 00 00 00 00 00 00 00 3b 5d 06 00 00 00 00 00 ........;]......
0030: 28 00 00 00 80 02 00 00 e0 01 00 00 01 00 18 00 (...€...à.......
0040: 44 58 35 30 00 20 1c 00 00 00 00 00 00 00 00 00 DX50. ..........
0050: 00 00 00 00 00 00 00 00 ........


It’s basically the same for everything I try to play, except for some really old Babylon 5 DVDs...