svchost.exe

Upon logging on to Windows I get a message that
svchost.exe has generated errors and wil be closed by
Windows.

Once this happens my computer slows down considerably and
I cannot perform certain applications. For example,
Outlook Express does not let me reply to messages.
I am told .."there is not enough memory ..."
and I cannot use the Search function (for files and
folders).

Essentially, it appears that the memory of the computer is
affected.

This could have been a virus that damaged some file.

Any sugggestions ?
Many thanks,
Nicolas