You can’t really expect anyone to diagnose your trouble based on such limited symptoms and absolutely no tech info? Based on the info you have given concerning the symptoms, your problem could be 10 to 20 different things.
I grabbed a modified magic 8 ball and it says that your trouble originates in a faulty ZX-81.
For better WAGs please give more info.
Computer make/model. Motherboard make/model. Ram. HDD info. Video card info. Modem info. ISP info. etc. . . .
The easiest way to compile most of the needed information is to run dxdiag. At the bottom of the dxdiag window will be an option to save the diagnostic test info. Save it. Then open the saved text file. Delete the info toward the top that has your name and such. Then copy and paste the report here. Yes it is big, copy and paste it all.
Then add your modem info, is your computer network wireless or wired, your isp info, info about the indications for the games performance meter just before LD and any other info you can think.
With all that info there are many who should be able to give suggestions.
gl
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The art of war is simple enough. Find out where your enemy is.
Get at him as soon as you can. Strike him as hard as you can,
and keep moving. - Ulysses S. Grant
Only the dead have seen the end of war - Plato