My friends pc that I built 2 years ago started showing no signal to the monitor and I noticed the LED lights on the MB (from L to R) the 1st one stayed on and the other 3 are flashing. I never could find the cause for sure, so assumed it was the MB or CPU from everything I read and asked around. Seems how they were under warranty I sent them back and they sent me what I'm assuming is a refurbished MB (MSI 970A-G46) but a new CPU(AMD FX 4300). I got the PC all put back together and it's doing the exact same thing as it was so now I'm back to being baffled and looking for help!

*I tested the Video card - (SAPPHIRE 100323-2L Radeon HD 6570 1GB 128-Bit DDR3 PCI Express 2.1 x16 HDCP Ready Video Card) in my working PC and the card worked.
*I tested both the memory sticks (Crucial Ballistix Sport 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model BLS2KIT4G3D1609DS1S00) one at a time and even tried my own memory card out of my working PC and still nothing.
*When the PC first quit (before sending MB and CPU back) I also tried her HDD (Western Digital Blue WD10EZEX 1TB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive Bare Drive) in my old PC and it booted up no problem.
*the tower is (RAIDMAX Altas ATX-295WBP Black Steel / Plastic ATX Mid Tower Computer Case 500W Power Supply)

Not sure what other info ya'all would need to help me figure this out, but I'm more then happy to get that info also if I didn't include it already!! Any help if MUCH appreciated because I certainly haven't figured it out yet!! :(