HL2 nocd error

[m00nce]

Ive just installed hl2 after a freakin hour! (DVD Version)
-Created my steam acccount
-Updated my steam account
-Entered cdkey to steam
-Connected to net (of course)

Installation is fine but then...........

When i try and run the game it says no-cd inserted (the disc is in the drive!)

ne1 else run into this problem? need help goin insane.

my m8 bought his version the same day from the same shop he installed no problem.
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My specs:

Winxp Home sp2
Radeon 9600xt 256
1.5g DDR Ram
2800 AMD processor
Lite-on 16X DVD Rom
D-Link DSL 504G Modem/Router
512 connection speed ADSL

My mates PC is very similar

 

[Varsity]

Yeah, some people have been reporting it. Talk to Vivendi.

 

[m00nce]

I uninstalled Sonic DVD and now my game will work...!!