when i log in it says i don't have antivirus

i have avast and it is up dated every day and many times whern i turn my pc on it says i dond have an antivirus on and avast is running no prooblem so i go to control panel and aloud avast and restart computer and it works , this did not happened to me before does any one knows why? and also two days ago avast disapear from my pc i had to downloaded it again how come? thank to anyone who can answer this question

do you have any other security programs installed?

no i don’t have any other that i know of do you mean like any other antivirus? sorry for my ignorance…

attach (not copy and paste) OTL diagnostic log. http://forum.avast.com/index.php?topic=53253.0

What os?
What avast & vps version?

so i go to control panel and aloud avast
Where exactly do you go? Avast isn't in the control panel.

i check the secuity centre on control panes and sasys i don’t hasve malaware protection

What version of windows do you have as the security centre sometimes gets forgetful

v8

Do you mean Windows 8 or Avast version 8?

windows vista

windows vista and avast 8

This may seem a silly question but do you actually have virus reporting turned on within the security center?

Have you checked the actual settings?

Try this http://my.opera.com/rejzor/blog/security-center-reset-1-0-released