My computer has trouble running hard drives

So,I've recently ordered a new gaming PC.

When I installed it everything worked accordingly until i checked my hard disk drives.My primary 120gb SSD was present but my 1TB seagate hard drive vanished.
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Upon further investigation i found out that my computer was still detecting it but it was constantly disappearing and reappearing in the hard disk drives section of "My computer".
When i tried to put something on the 1tb drive it only accepted around 1 GB and if the file size was bigger the loading bar would just stop moving.
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I contacted the company i ordered the computer from and they shipped me a new hard drive(Same one). Tried it out, same exact problem.So i tried a different model and same exact problem.
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My best guess is that my power supply is not good enough to run anything more on my computer ,but I'm not too sure.(STANDARD 800 WATT)If anyone knows what's going on, some help would be fantastic.
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Here are my pc specs :

Processor AMD FX-8120 CPU (8x 3.10GHz/8MB L2 Cache)

Memory 8 GB [4 GB X2] DDR3-1600 Memory Module

Video Card AMD Radeon HD 6850 - 1GB - CrossFire Mode (Dual Cards)

Motherboard Gigabyte GA-970A-D3 -- AMD 97

Power Supply 800 Watt -- Standard

Primary Hard Drive 120 GB ADATA S510 SSD - Single Drive

Data Hard Drive 1 TB HARD DRIVE -- 32M Cache, 7200 RPM, 6.0Gb/s - Single Drive