Dell Inspiron 15R 5537: Keyboard issues

I usually type with both hands. I've had this laptop (Win 8.1) for quite a few weeks.

I frequently find some of the keys (mostly on the left side) of the keyboard are not registering, in particular these letters: E, C, D, R, A, S, B and O are problem keys. E and O are the worst ones.

The problem gets worse when I type a bit faster than usual.

I'm having to either type much slower than usual or proofread extra closely (which I never had to do when using my old laptop before it died) because of missing letters.

It's maddening. I've had this problem right at the start with this laptop, and it hasn't improved since.

Here's an example of the issue when typing at normal speed with both hands, without any corrections.

[unedited] This is just an xample of the issue with the kypresses not registering whn typing with both hands. The letter E gives m the most grief when typin. Somtimes the poblm occurs with other letters. I hav been typing for donkeys years and have rarly ha thi issu thi bad.

[corrected version] This is just an example of the issue with the keypresses not registering when typing with both hands. The letter E gives me the most grief when typing. Sometimes the problem occurs with other letters. I have been typing for donkeys years and have rarely had this issue this bad.

I've checked the keyboard and there aren't any defects that I can see. No crumbs or dust or whatever. I've checked the keyboard settings in the control panel, and the only settings available are: repeat rate and cursor blink speed. Dell doesn't include proprietary settings for the keyboard.

How can I fix this issue? Is the keyboard simply not sensitive enough to detect some of my keypresses?