Keys not responding

[Pastore]

Advent QC430 Notebook.

Having problems with the majority of top line of 'letter keys' not consistently working in lower case (particularly the 'w e r u i o p' keys), although they seem fine in upper case. The 'left arrow' key is also often problematic.

Sometimes they work fluently if I switch from mains to battery but usually only a temporary solution.

Any ideas/suggestions appreciated.

Thanks.