Dell Inspiron All in one model 2305 solid amber power light, display dark blue

I get good video in composite and usb  input mode. Hard drive and optical drive starts up. when powering up in Inspiron input mode, but display stays dark blue and solid amber power button.

I have tried reseating ram, and hard drive connectors. Repaced cmos battery and did the power drain holding down power button for 60 seconds with power cord out. Appears to be in sleep mode.

Questions: Could the display still function as a monitor if the motherboard is bad? It has excellant picture when connected to tv as monitor.

I am looking at a refurbished same model computer w/o operating system. If I put my hard drive in the refurbished one will it work. Or will I have to purchase a new operating system?