im experiencing a similar problem, with a comprio E750 card in DH57JG, the card most of the time is not detected by the bios and is never seen by windows.
I can confirm the same problem with a Hauppauge HVR-2200 PCi-e card.
My Specs are :
DH57JG (Latest Bios 0537)
2*2GB Kingston DDR3-1333 Value Ram
Power Supply 200 TFX
TV Tuner Hauppauge HVR-2200
Just an update, tried a different blackgold tv tuner in the slot and this one seems OK. Still not sure where the fault lies, seen as two differnet makes on card where showing exactly the same problem but now this one seems good.
Problems with TV tuner cards exist for hybrid sleep in particular. While disable of C1E reputedly fixes some issues I am currently using S1 rather than default S3 power state in BIOS to avoid problems. That is for DG45ID with Q6600 CPU and Hauppauge 1250. I have only seen the problem when using the recording feature. S1 in Win7 provides the option for manual hibernation if one would rather use that than sleep and manually saving and closing apps. Reinstallation may fix issues where the card is not detected. Multiple restarts can be required for proper detection on installation.