As someone who routinely runs into this issue, I’ve also been wondering about this for the last few months. I bought an old Dell E176 on Ebay for console access. Recently when I needed it for upgrading a few computers, this became a issue. After reading through the forum posts, it’s clear that Dell monitors have problems with there memory settings (in the monitor’s hardware, not the PC) and coming out of power save mode.
Solution
Unplug the power cord for the monitor from the wall and wait for about 10 seconds, then replug-in the monitor. This should force the monitor to come out of sleep mode and re-calibrate it’s settings. Unplugging the VGA/DVI cable doesn’t do this.
Afterwards, set your desktop power settings to never sleep the monitor. Otherwise, do the aforementioned again.