New GPU, no Post Beep, no Display

[Elias Somero]

First off, here are my current Specs:

GPU: 2GB AMD Radeon HD 7700

CPU: Intel Core i3 Dual-Core Processor 3.1 GHz 3 MB Cache

Hard Drive: 250GB, 7200 RPM, 16MB Cache

Motherboard: GIGABYTE GA-H61M-DS2 LGA 1155 Intel H61 Micro ATX Intel Motherboard

RAM: 8GB (2x4) 1600MHz

PSU: Antec True550w

I recently bought a HIS 7870 (http://www.amazon.com/HIS-Mini-DiplayPort-Express-Graphics-H787Q2G2M/dp/B007HYIRES) because I wanted to upgrade my computer. I had to buy a PCI-E adapter because I only had one plug and this needed 2. It connects to my plug and splits it into 2. Both plugs are in, the fan of the GPU is on, but if I turn on my computer, I get no display and no Post Beeps. After trying some more I have to switch back to my old GPU so I can use my computer again and usually it says the BIOS is corrupted and will recover. It of course did and everything is fine.
Any suggestions?

 

[scout_03]

this look like your psu could not handle the card with only 18 amp on the 12 volts line that most be the old 550 model .

 

[Elias Somero]

Yes, the PSU is quite old, about 10 years, with about 5 years of total use