Lol, thanks for the compliment Critical_Fallacy though i'm not sure how much of a help I could give. Do you patrol this education forum every day?

To the OP, it's quite common and I bet every single student doing graduate studies (especially in natural science) has encountered during research, and will continue to encounter throughout his/her research career. There will be times when everything is going well, all the results are positive and you're motivated to keep going.

And then there is the other end like where you are now.

My first suggestion to you is to immediately stop whatever experiment you're doing. You're tired, demotivated and not focus. You're running it just because that's what you're supposed to do. I'm quite sure you're pretty sick of looking at the experiment setup, parameters and preparation and are just running through the motions. In other words, you're just repeating whatever that was not previously working. This is equivalent to proofreading your thesis so many times that your eyes tend to skip over words and overlook obvious typos.

Take a break. Take the weekend or a few days off. Go on a holiday or hang out at the mall. Don't think about your research for a few days. Go meet up with your friends. Or even simply just get a haircut or change your hair! As you acknowledged that you're stuck in a rut! Even small changes will have amazing effects.

Once you come back refreshed, relook your experiment from the start, not just from the previous step. Make sure you understand the theory and rationale behind it. If the theory is fine, what about the preparation and the steps? Has anyone done this before in your department? Or look for help online: try posting in scientific forums e.g. researchgate or protocols forum etc.

Or you can try to run the experiment again, starting from scratch. New fresh samples, new reagents, sterilised and clean pipettes, clean or different machines etc. Or even ask your someone else in the lab to do the protocol for you to make sure it's not your hands or something obvious that you inadvertently overlook.

Are there any alternative methods to your experiment? Is it possible to conduct this alternative method? Can it be outsourced to a research service company? Sometimes spending a bit more money is worth it rather than repeating an experiment by yourself and wasting reagents while not yielding any result.

Whether you're cut out to be a researcher, is not a matter of luck alone. It boils down a lot to your passion and aptitude. Remember that you're not alone, you should always discuss any major problems with the people in your lab or your boss. Be firm to your boss, if he/she just says "Just repeat it. It will work." Seek help and advice from other people in the lab, some of them might have more experience and knowledge at a certain protocols compared to your boss.

Good luck!