300w to 800w Power Upgrade, No Signal to Monitor

Hi There,

I was about to upgrade my "new-to-me" refurbished desktop from on-board graphics to a Radeon 290 4GB card. Out of the box, stock PC, everything ran fine, I downloaded some games waiting for the Radeon 290 graphics card to come in the mail. I did some reading and decided I should upgrade my power supply from the stock 300w to a new "Apower AK 800w" power source since I planned on getting more drives etc for media recording/editing purposes. I unplugged stock, and installed the 800w power unit. I tried to install the graphics card as well and turn on the unit with new and improved graphics and wattage...

Blank screen both HDMI and VGA on graphics card. I tried on-board as well next. Same result blank. I decided I should go back to just on board graphics and trouble-shoot that way. Even with on-board graphics and no card installed same result.

I read some forums on here and many other places that suggested I (hold the cases power button down for 30mins-1mins, pulling out mobo battery, and unplug everything then plug-in in special order, as well as only run 1 stick of ram, and unplug drives for minimum required features to display BIOS on monitor.) None resulted in VGA or HDMI signal from mobo.

I will try to put my old power supply in and see if that fixes it, I have a hunch its a power issue or maybe my mother-board cant handle the power supply, even thought the customer service rep at Dell said higher watts "won't hurt anything."

Please take a look and let me know what you think I should try, currently I cannot even get to BIOS or load any screen at all either HDMI or VGA since installing APOWER 800 source.


----------HARDWARE DETAILS

Mother-Board: MIH81R/Great Bear
13040-1M
CGDJT $FA


New Power Source: APOWER Series 800
AK 800w ATX/SATA

Removed Power Source: Dell B300nm-01
Ref No. DE-XD301MGR

Graphics Card (I tried to install): Radeon 290 4GB PCI

Dell Inspirion -Mini Tower-