If you can't even start the graphical installer, when you are in the initial text installer screen, select 7 "Run installer in VESA mode":
Most of the times this is enough. If you can't even get this screen, this is probably due to a fatal trap 12 error. You first can unplug as many devices as possible, for instance unplug webcams, scanners, printers, USB mice and keyboards, keep the bare minimum hardware. If this solves the problem, start plugging more hardware little by little to see which one is causing the problem.
If this doesn't solve your problem, try disabling ACPI the next time you start up on the very first black & white screen. Additionally, your download may have experienced a problem and PC-BSD's installation CD-ROM may be corrupted. To check integrity of your .iso file, you can either use the md5 tool on Unix systems typing md5 <name_of_file> in your terminal or you can use WinMd5Sum for MS Windows. You will find the md5 checksum on the download page of PC-BSD for each .iso file. For each of them, the checksum reported by either md5 or WinMd5Sum must be the same as the checksum listed on PC-BSD's download page.
More troubleshooting entries will be added on this page over time. Let's discover PC-BSD's workspace now.