(SOLVED) Suddenly, Selecting Sleep shuts down the computer

Sleep definitely shuts the computer down. No matter what I do in Power Options, when selecting Sleep, computer is definitely off. How can I be so sure?

Well, in the past when Sleep was working, there would always be a blinking blue light emanating from the computer's on/off button and when bring back from Sleep all I would have to do is tap any key or left click my mouse and without any hassle, open programs would come back. However, now when selecting Sleep, no blinking blue light, no awakening when tapping keys or left clicking mouse. To open computer I have to depress the on/off button and when the computer comes to life there is that Windows Error Recovery screen and when Firefox is opened, I'm told that it crashed and if I wanted to restore stuff.

The results of a Hibernate shut down are quite different and look to be normal. No blinking on/off light, but have to depress this button to get things started. Screen says Resuming Windows instead of Starting Windows as it did when using Sleep, there is no Windows Error screen, and I'm not asked to my user password. Also, Firefox opens without any "crash" alert.

I guess i can live with using Hibernate, but it is a real PITA compared to Sleep and I would much prefer to get to the bottom of this so that I can use Sleep.

EDIT: Problem Solved

Problem Solved.

Took the bull by the horns and entered BIOS and went to Power Management Setup. S1/S3 were all enabled for mouse, keyboard and USB, there was no S2. Suspend Mode was set to [S3 (STR)]. There was an option to set it to S1 (POS)], which I did, and then finished booting. I then set all my Power Options (within the Control Panel) to their defaults, backed out to the desktop screen, clicked my mouse button to bring up closing choices and selected Sleep. And, Sleep it was!

Now I'd like to know:
1. What are the meanings of SRT and POS and why did this work?
2. As Sleep was working for about 4 years, what could have caused things to change in the BIOS...here I am assuming that the BIOS setting was originally S1???