old Panasonic TH-42PV500E
I'm sitting next to my 2006 TH-42PV500E (with large floor stand). Sometimes I connect it to a desktop PC, but I use the HDMI output from my GPU, not VGA (via DVI). I tend to use the plasma TV as a second display, with 24in monitor attached to the DVI output of the computer as the primary display. Both screens run at different resolutions, with no intervention on my part.
I know the Panasonic is a native 720p HD-ready display. On page 41 of the manual it states the computer VGA signal display resolution is 1,024 × 768 dots when the aspect mode is set to “16:9” (TH-42PV500E) and 768 × 768 dots when the aspect mode is set to “4:3” (which I doubt you're using).
1024 by 768 is an old computer screen resolution with an aspect ratio of 1.333 and square pixels? on an old-fashioned 4 by 3 monitor or non-widescreen TV.
A 16 by 9 TV has an aspect ratio of 1.777. When displaying 1024 by 768 pixels on the Panasonic, the computer's GPU pixels will be stretched horizontally to fill the 1.777 aspect ratio screen, forming small rectangles. This is part of the reason why this TV is not ideal for computer use, because you're not mapping pixels at 1:1 from the GPU to the TV.
In addition, if the TV is only capable of displaying 720 lines, what happens to the extra 48 lines of a 768 signal. It might explain why you lose the Windows menu bar off the bottom of the screen. I seem to remember when I was using the VGA output from a media PC back in 2008, I invoked the under-scanning option in my computer's graphics driver, to squash all the VGA lines into the 720 lines available on the TV. This further degraded the quality of the picture, because 768 GPU lines don't match 720 TV lines 1:1.
It seems likely that when I used the HDMI input to the Panasonic earlier this year, my Windows 10 computer set the secondary display to 720p, matching the number of lines on the TV screen exactly. That's a good reason to use HDMI instead of DVI/VGA, if your GPU has an unused HDMI output. I would have thought the bandwidth on HDMI and VGA signals would be similar, so the main reason for blurring is failing to match pixels 1:1.
I've long since switched to a 55in OLED Panasonic from 2017 for my main viewing at 4K HDR using a media PC. The old plasma TV is relegated to the computer room and I have a new 42in OLED Panasonic in the bedroom. By the way, I recently discovered the plasma TV consumes 20W of power in standby mode. It's a good idea to switch it off properly at the front, so the amber LED isn't shining.
Do i need to have 2 saved information files about my Tvs in Windows?
I don't think that's the way Windows works. I just let Windows sort out the "best fit"each time I connect to HDMI on a laptop or desktop. The computer asks the TV what aspect ratios and scan rates it supports via HDMI, then sets the most appropriate option. VGA is a fixed "take it or leave it" output. You have to manually change the VGA port's output resolution and scan rate to suit the TV. What the TV does with incorrect VGA resolutions is in the lap of the gods.
Toshiba 46tl963 from 2012
If you're using a VGA input on the Toshiba (I haven't checked the spec.) and it's Full HD, you might be using a higher Windows resolution, e.g. 1280 by 1024, or 1366 by 768, which is incompatible with the Panasonic.
