When I bought my computer, it came installed with Windows XP and all other programs. I tried getting service pack 2 and was unable to install it as the XP was not the original.
Ever since the computer has been displaying XP not genuine and has basically made all the WMV files and video capture in WMV formats unusable and unreadable by all media players in the computer.

Any advice, help folks?

just what u have to do is make a registry by yourself
there r the steps

1) open new note pad n name it "WindowLicence"
2) copy the following code in it:
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\WPAEvents]
"OOBETimer"=hex:ff,d5,71,d6,8b,6a,8d,6f,d5,33,93,f d
"LastWPAEventLogged"=hex:d5,07,05,00,06,00,07,00,0 f,00,38,00,24,00,fd,02

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion]
"CurrentBuild"="1.511.1 () (Obsolete data - do not use)"
"InstallDate"=dword:427cdd95
"ProductId"="69831-640-1780577-45389"
"DigitalProductId"=hex:a4,00,00,00,03,00,00,00,36, 39,38,33,31,2d,36,34,30,2d,\
31,37,38,30,35,37,37,2d,34,35,33,38,39,00,5a,00,00 ,00,41,32,32,2d,30,30,30,\
30,31,00,00,00,00,00,00,00,00,0d,04,89,b2,15,1b,c4 ,ee,62,4f,e6,64,6f,01,00,\
00,00,00,00,27,ed,85,43,a2,20,01,00,00,00,00,00,00 ,00,00,00,00,00,00,00,00,\
00,00,00,00,00,00,00,00,00,00,00,31,34,35,30,34,00 ,00,00,00,00,00,00,ce,0e,\
00,00,12,42,15,a0,00,08,00,00,87,01,00,00,00,00,00 ,00,00,00,00,00,00,00,00,\
00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00 ,94,a2,b3,ac
"LicenseInfo"=hex:9e,boyfriend,09,d0,3a,76,a5,27,b b,f2,da,88,58,ce,58,e9,05,6b,0b,82,\
c3,74,ab,42,0d,fb,ee,c3,ea,57,d0,9d,67,a5,3d,6e,42 ,0d,60,c0,1a,70,24,46,16,\
0a,0a,ce,0d,b8,27,4a,46,53,f3,17
3) close the file
4) right click on the file -> properties -> opens with change -> go to "windows" folder then u will find file "regedit" select it
then double click on the file it will ask u something say yes -> OK

Congrats your problem has been solved

Above will allow you to get your copy genuine, which is a good idea
Your issue is your having problems with codecs, you need to download the codec and install them and you shouldn't have nay problems playing anything, here is a link and the file is free
Free-Codecs.com : Download K-Lite Codec Pack 3.6.5 FULL, K-Lite Codec Pack 3.6.5 STANDARD, K-Lite Codec Pack 3.6.5 BASIC : K-Lite Codec Pack is a collection of codecs and related tools