There's actually a big clue in the message: "Hardware reserved".
If checking/unchecking the "Maximum memory" checkbox under Windows isn't helping, the culprit may be the default BIOS settings, which can reserve excessive RAM for graphics hardware.
In my case, Windows reported that 1.1G of my installed 8G RAM was "hardware reserved":
I fixed it by changing the BIOS setting. The naming or menu details may be different in your BIOS, but here's the story in my case. Under the Advanced settings, go to Advanced Chipset Configuration:
Under Advanced Chipset Configuration is a setting called UMA Frame Buffer Size. This controls how much of your RAM is reserved for your graphics hardware, and by default may be set to Auto, which will decide an amount based on how much RAM you have installed and—depending on your needs—may reserve far more than necessary:
For general use, set it to 256M:
The result in Task Manager: