and click in Memory Support List and make sure your memory is listed.
to make sure your thermal compound was applied correctly (unless preapplied to heat sink).
Your video card:
HD 6770 System Requirement:
PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard
450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended (600 Watt and two 6-pin connectors for AMD CrossFireX™ technology in dual mode).
Certified power supplies are recommended. Refer to http://ati.amd.com/certifiedPSU for a list of Certified products
Minimum 1GB of system memory
Installation software requires CD-ROM drive or DVD-ROM drive, a keyboard, a mouse, and a display
DVD playback requires DVD drive and a DVD
Blu-ray™ playback requires Blu-ray drive
For an AMD CrossFireX™ system, a second AMD Radeon™ HD 6770 Graphics card, an AMD CrossFireX™ Ready motherboard and one AMD CrossFireX™ Bridge Interconnect cable is required
Use of 3 or more displays with AMD Eyefinity technology requires a DisplayPort-capable panel or an AMD Eyefinity validated dongle. See http://www.amd.com/EyefinityDongles for a list of validated DisplayPort dongles.
Note:"450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended"
Your power supply:
Corsair CMPSU-800G Gaming Series GS800 800W Power
Form Factor: ATX
SLI/Crossfire: SLI Ready
Energy Efficiency: 80 PLUS
Fan: 140 mm
Input Voltage: 90V ~ 264V
+3.3V: 25 A
+5V: 25 A
+12V 1: 65 A
-12V: 0.8 A
+5VSB: 3 A
MTBF: 100,000 Hours
20+4-Pin Connector: 1
Motherboard Connector: 24-Pin
4-Pin/8-Pin EPS Connector: 1
Motherboard Power Connector: 4/8-Pin EPS x1
8-Pin PCI-Express Connector: 4
4-Pin Floppy Connector: 2
4-Pin Peripheral Connector: 8
SATA Power Connector: 8
Note: " +12V 1: 65 A" and " 8-Pin PCI-Express Connector: "
According to the specs, your wattage should be enough, but your 12 volt amperage may not be enough (65Watts instead of 75Watts) PLUS you need a 6pin PCIe connector and you have an 8 pin PCIe connector that does not appear to be convertible to 6pin as far as I can tell. Do you have a 6pin plug connected to your video card?
Are you able to test the power supply on another working computer?
You have to be a little bit crazy to keep you from going insane.