BebuLamar

The M lenses which didn't work as per the OP are completly compatible with the K1000. Haven't heard back from the OP but I have the feeling the OP has the K100D instead of the K1000.

lamiaceae Loc: San Luis Obispo County, CA

Yes, it all would make more sense if that were the case. Hope it is and all he needs is a change or two in his set up menus.

Lucas Loc: Japan

This could be because the K1000's light meter relies on aperture information that is communicated through the contacts on Pentax-A lenses. If you're using Pentax-M lenses or ones that don't have those contacts, this might be why the light meter isn't working right. Something you could try is third-party lenses that have similar communication abilities to Pentax-A lenses. Failing that, using an external light meter for exposure readings could help as well. Lastly, if it's the camera's light meter itself that's the issue, seeking out professional assistance (either via repairs or by contacting the manufacturer) would be best.

Overall, the K1000 is a fantastic camera and it's worth taking the time to figure out the best way to use it with your preferred lenses. Here you can find lenses that are compatible with Pentax K1000: https://lensespro.org/pentax-k1000-lenses/
Good luck and happy shooting!