The last time I had troubles with sleep mode, it turned out to be the video driver software. Upgrading to the latest driver for my ATI video chipset fixed the problem.

Of course, I was on a laptop, where "upgrading to the latest ATI chipset driver" was a bigger issue. If you're on a desktop system, no worries.

The DRM software remover installation is probably a coincidence. I don't imagine such a piece of software needs to install device drivers, services, or resident programs. But if it does, it might be worth looking into as a possible cause.