VBS script keeping old values even though I changed them

I am running the script below to keep my computer from going to sleep:

set wsc = CreateObject("WScript.Shell")
Do
    'Five minutes
    WScript.Sleep(5*60*1000)
    wsc.SendKeys("{NUMLOCK 2}")
Loop

I am trying to change the key to replace the key to be sent form NumLock to F8 but no matter what I put in the script, once I save it and run it, it keeps sending NumLock. Do you know why?
Thanks in advance