Before replacing the video card, I would try all software troubleshooting options. For instance, try updating your video driver. Here is the latest from HP for your PC: http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=pv-62691-1&lc=en&dlc=en&cc=us&lang=en&os=2093&product=3644699
Also, what monitor do you have? You may need to install a new monitor driver or other monitor software.
--Although I am an HP employee, I am speaking for myself and not for HP.--
I have a HP a6330f Desktop AMD Athlon 64 X 2 Dual Core 5600+ 2.8 GHz, 3.0 GB RAM, 32 Bit OS, Vista Home Prem Serv Pack 1, Verizon DSL for internet. Randomly a little box pops up in the lower right side of the screen stating "ANALOG", the the screen flashes on and off. I try to reboot most of the time it continues to flash on and off but does reboot. It does eventually stop but then starts up again at any random moment. I have a NVIDIA GeoForce 6150SE nforce 430 video card. I bought this system 1 yr ago Jan. Does the Video card need replacing already?!