Hi and a big thanks to everyone who has responded.
After a tiresome and frustrating weekend, trying all i know and following the advice offered here, i have finally hit upon the solution to my problem.
In my original post, I mentioned the problem arose after I had recorded vinyl albums to CD. I was firmly convinced that the program (LPRecorder) was in some way to blame for the failure of the Hibernate mode.
Well, after running powercfg -energy in cmd.exe, one of the errors listed was:
<HTML><META HTTP-EQUIV="content-type" CONTENT="text/html;charset=utf-8">
<p class=log-entry-header>System Availability Requests:System Required
<p class=log-entry-description>The device or driver has made a request to
prevent the system from automatically entering sleep.</DIV>
<TD><SPAN class=detail-name>Requesting Driver Instance</SPAN></TD>
<TD><SPAN class=detail-name>Requesting Driver Device</SPAN></TD>
<TD>High Definition Audio Device</TD></TR></TBODY></TABLE></DIV>
When I saw High Definition Audio Device I racked my brains to recall exactly what changes I had made there when recording the LPs. Then I remembered that I had ticked a box to allow me to hear the audio from the Line In. I went back to untick that box and rebooted. I then reset the power settings to let the PC sleep and lo and behold it worked again.
I nearly came undone when, to verify that this tick was the offending item, I ticked it again and sure enough Hibernate function failed again. The problem was that after unticking it again, the function did not restore.... However, after a bit of fiddling around and rebooting, it did again and it is now seemingly OK.
I hope this solution is a help to others who come to this post looking for assistance,
Thanks again to all who replied,