I have an old PC I want to sell, how much is it worth?

I have an old Lenovo ThinkCentre A62 in decent condition with a broken CD Drive.

Here are my questions:
- How much is it worth as is?
- How much is it worth if I replace the drive? (I have a spare)
- Will it sell for more as a whole unit or as parts?
- How much is it worth with the monitor and keyboard?

I know it's a lot to ask but I'm really unsure of what it's worth. I've looked online but couldn't find anything. Any help is appreciated.
Added (1). Specs: http://www.cnet.com/products/lenovo-thinkcentre-a62-tower-9935d1u/specs/
Mine has 2GB ram

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