While browsing online the screen suddenly changed to a mesh of pink dots. There was no response to any action, so I pressed the restart button. On attempted restarting the screen displayed multicolored vertical lines. An attempt to boot from an MS-DOS startup floppy produced alternate flashing colored screens.

Any suggestions anybody?

Do you have another monitor to try?

I've tried the monitor on another computer and it works fine

Next suspect is the graphics card.

Do you have another card or does your computer have on-board graphics?

I have an old computer (somewhere!) with I hope a graphics card. I'll try a swap. Thanks for the advice!

No problem. Let us know how it goes.

Removed GFX5500 from the faulty computer. Tried an old nVIDIA card (not sure of model, but it worked in old computer). Nothing on monitor at all, but it sounded as if windows was starting, with usual windows noise. I've checked monitor lead again. What next?

I've purchased and fitted another graphics card. Everything now works OK. Thanks.

Thanks for the update.

Let us know if we can help further in the future.