Hmm have you installed front row? Mine did excatly the same, a reboot solved the problem though... I suspect the front row install to be the problem (in my case anyway)
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- iMac g5 2ghz, 1.5gb ram.
- eMac 1ghz (clocked at 1.27): 1gb RAM, Dual Layer Pioneer DVD +/- RW, 80 gb HD, 160 & 250 external Lacie FW HDs. And modified cooling.
- iMac 600 mhz
- b&w in atx case, with sata drives :p
- PowerMac g3 b/w - with atx psu
- PowerBook G3 Wallstreet