Since there were no NUC products that utilized 1st gen Core processors, we can't help you with only the information provided. In general, what you need to do it contact the manufacturer for your motherboard and ask them this question (note: many manufacturers have web pages that provide this information). If this is an Intel Desktop Board, let us know its name and we can point you to the processor compatibility document specific to this board.
Hope this helps,
Again, this forum is for Intel NUCs, and the following advice needs to be checked for applicability before attempting the suggestions.
1. Find the manual for your BIOS, from the motherboard manufacturer or the PC manufacturer.
2. Look up the BIOS beep codes.
3. Determine whether you feel comfortable with implementing the suggested solutions for the particular beep codes that you encountered on your PC.
This page may serve as a guide, but it may not apply to your PC. According to it, 1 long and 2 short beeps signify video card failure. There is a chance that you bumped or pushed on the video card while changing the CPU chip.
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Intel Customer Support Technician