Wierd problems with my newly purchased Asus Radeon HD 7750

Hi all,

When i bootup to Windows 8 with my new Radeon HD 7750, my computer's optical drive is not listed in My Computer and Device Manager. But, i can see the optical drive listed in BIOS. Repeated restarts did not solve this issue.
Secondly, my graphics card is listed as 7770 after i downloaded and installed the graphics drivers from the AMD website. (Is 7750 is a nerfed version of the 7770?)
Lastly, after about 1 hour, the screen just went black.

When i replace it with my old graphics card, Nvidia 8800GT, the optical drive reappears in the My Computer and Device Manager and the computer works perfectly fine.

I am using a rather old core 2 duo series processor (Intel E8500), brand new ASUS motherboard and rather old ANTEC True Power Trio 550W Power Supply.
I was initially suspecting the power supply assuming that the optical drive stops appearing because it's usual power supply is being sucked to the 7750; but the power requirements of both cards are the same and i also heard that the 7750 utilises low power for a graphics card. So it seems wierd the that computer works perfectly fine with the 8800GT.

My question is, will i be wasting my money if i go for a new power supply to solve this issue because the problem is something else? Also, i have no access to spare power supplies for testing.