I try and open it and it says:

Unable to set specified graphics mode because: Overlays not supported!

Now trying to default back to VGA...

It then crashes and says:

Abortion in file .\System\ContentFile.ccp, line 508, because: Failed to load data file object with the following path and name: Base.rte/GUIs/Sounds/MenuEnter.wav

The last frame has bee dumped to 'abortscreen.bmp'

I have tryed redownloading and installing several times does anyone know how I can fix this!

Those "I cannot find this sound although it exists you just suck so I wont work" bugs are annoying.
Tried rebooting?

I've tryed loading the game several times, rebooting my computer and loading the game redownload and install 3 times, nothing works.

This is an old problem, various fixes suggested in the past include Restarting CC, Reinstalling CC, Rebooting, Runnin Checkdisk and the above.
As you have tried most of those I suggest the above...

It now comes up with:

Unable to set specified graphics mode because: unsuppoted colour depth!

Now trying to default back to VGA...

It then unlike before goes through all the loading and then crashes?????????????????????????????

you probably accidentally closed down the svchost.exe process. I did the same thing. if restarting dosent work, open media player and try playing music.

wow it actually worked thanks

my souloution?

yes playing music in media player actually made cortex command work!!!!

I doubt it. that was a way to diagnose the problem. what i said probably happened is that you closed down the process your sound card used to make it work. the same thing happened to me a few days ago.

nope I played music in media player, I opened it it came up with an error message but still worked, now it dosn't come up with error message, although the games running a bit slow.

that is FREAKY. that should NOT happen.

Yeah I installed new video and sound drivers, got a differant error message and so I opened media player and it came up with a differant error message again but didn't crash, my only problem is it runs it bit slow every now and again.

sound driver issue with CC are hilarious. grif couldnt touch the game for ages because his laptop didnt have drivers, and CC wont run without a way to pump sound into your computer, regardless of the volume being off (ingame) or not.
in other news, CC running slow is an issue almost everyone has with it.

yeah it's wierd cause 1 moment theres dropships exploding everywhere and dummeys shooting at each other with no lag and then your just walking down a bunker with no explosions or things happening and it lags beyod belief?!?!?!?!?!?!?! and then a minute later goes back to normal!?!?!?!?!??!?!