I just made my first pc about 2 weeks ago and the problem I been having is sometimes the pc will not see the usb ports and my screen goes black with the orange power light on. Like when you turn on the screen and have it disconnected. This all happens random times, it can be 20 mins after I turn on the PC or after I leave it on for 3 days. What can cause this to happen. I didnt OC anything. Here are the hardware parts.
MSI 890FXA-GD65 AM3 AMD 890FX SATA 6Gb/s USB 3.0 ATX AMD Motherboard
CORSAIR XMS3 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
Microsoft Windows 7 Home Premium 64-bit 1-Pack for System Builders - OEM
PowerColor AX6850 1GBD5-DH Radeon HD 6850 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFireX Support Video Card ...
AMD Phenom II X4 965 Black Edition Deneb 3.4GHz Socket AM3 125W Quad-Core Processor HDZ965FBGMBOX
RAIDMAX HYBRID 2 RX-730SS 730W ATX12V V2.2/ EPS12V SLI Ready CrossFire Ready Modular Modular LED Power Supply
I would start with the usual suspect which would be the Power Supply. It could be dropping voltage on the 12 volt rail resulting in the failure of your USB ports and random lock ups.
Another possibility is that there is something shorting in your case. Check the various internal cabling especially the USB cabling. If there is something shorting out there it will cause your PC to lock up.
Third possibility is that you have a USB device plugged in which is causing issues. Try removing the various USB devices on your system and see if the problem remains.
Start with the PSU though. That is where problems often reside.