How to check M6600 parametrs without access to systems?

If you are unable to boot the laptop or even to access BIOS, then I can think of two ways:

• Login to your Dell account to see if the original purchase invoice is there, showing specs of installed hardware;
• Open the laptop case and physically look at each component to find manufacturer/model information which you can research on Internet. RAM and drive should have their capacity printed on them.

This Dell document will show you that laptop's specifications, but of course some categories such as RAM and storage had various options available.

Follow the disassembly and reassembly steps in Dell's Owners Manual.
Look on YouTube for videos showing disassembly of your model. But, be cautious with them, as some use steps or methods that are not appropriate. Use the videos to add to your understanding of what to do, but follow the steps in Dell's manual.

Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. It's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard. (Repeatedly touching a metal case part is not sufficient mitigation with modern components.)