I have owned my Dell Inspiron 15-3521 for a little over a year. Last week I bought a Samsung S22C300 HDMI monitor and connected it to my laptop for dual monitor use. Now, when I disconnect the laptop from the monitor to use elsewhere, my laptop randomly shuts down, (meaning it immediately loses power - not that it goes through the normal shut down process). It does not restart. It will not turn on until I either plug it into an outlet or connect the monitor to it (via HDMI, no power adapter necessary). Battery diagnostics say the battery is performing normally. I removed the battery and held the power button for 60 seconds with no results. Overheating is not the issue, as it does not shut down during the conditions listed above. I have never encountered this issue before; I have used the HDMI port to connect my TV with no problems.
Tonight laptop was completely charged when I disconnected it. It shut off within five minutes. I hit the power button and only the indicator lights lit up, (all blue indicating no problems). Screen did not come on, however, and the indicator lights went off in two or three seconds. I immediately plugged the monitor in and hit the power button. Laptop operated fine. I have been using it for two hours, now, with no power adapter. Battery indicates 3 hours of power left. (No problems so far...until I disconnect the monitor).
Running Windows 8.1 64 bit
Intel Core i3-3227U CPU @ 1.90GHz