it sounds to me that your processor chip or you fan to it is proberly loose,i would get someone to check this also check to see if your memory has come loose.It might just save you a bit of cash:
I have an older Dell computer and monitor. Just recently moved and attempted to set up system at my new house, but now the CPU won't communicate with the monitor. I used Dell's website troubleshooting to determine if the problem is with the CPU or the monitor, but both components check out as working properly, individually. CPU diagnostic system lights on the back of the unit are all green, which indicates the CPU is operating properly. Keyboard lights are lit.
Chatted online with Dell tech, who suggested it may be the power supply or the M/B, and my system is out of warranty, so I'd have to pay for the parts, but if that was the case, why are the diagnostic lights indicating the CPU is operating properly?

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