The HTPC we run has been through a few incarnations, currently a quad core Q8300 it’s more than ample for streaming and DVD playing, piping music to the living room, etc etc.
The ATI Radeon HD is the second GPU to be plumbed into it after an AGP -> PCIe Motherboard type upgrade.
The OS drive was a PATA, which was fine, but after a screwup on another build project, I had a SATA and needed a PATA, so a swapout was required.
The OS HDD swap was easy, using Acronis makes such things a sub 10 minute job if you always keep OS drive backups of your machines.
Turning the machine back on, everything initially seemed fine, but it turned out that there was no sound being delivered through the ATI 5450 HDMI connector to the Television.
After a lot of false starts around the internet during research, what worked for me was turning off the, presumably clashing, motherboard sound driver in BIOS (which is in the southbridge settings).
Disclaimer: BIOS can fuck you over, be careful, and it’s not my fault. Change things one at a time and remember what you did. That shit will bite you.
Good Luck