I know you said you uninstalled the old card, but did you uninstall the old drivers as well? I think you may need to eliminate all video drivers from you system(amd for sure, possibly intel or nvidia if that's the igp). Windows will use the basic video driver while you install the new driver package. I don't know if you were updating drivers with your old hd3870. If you were, is it possible the new card would work with the older driver? If you haven't been updating your drivers over time(removing the old before installing the new), maybe this is a procedural problem and the above stated process should fix things.
follow these steps....
2...boot in safe mode and remove all drivers using driver fusion
3..restart in normal mode and clean all registries using ccc cleaner
4...reboot and install new drivers..
The probem now seems to have escalated.
I cannot now access my PC at all.
The system boots up but the monitor will not start. All I have is a green flashing light on the monitor as if it is waiting to link up with the PC.
Is this now a monitor problem after all. Would a new HDMI monitor fix the problem?