What is wrong with my computer?

My computer keep pup up these kind messages(every 5 minute). One of them is like this:

“Message from SYSTEM to ALERT on 2007-10-3
STOP! IMMEDIATE ATTENTION REQUIRED
Windows has found CRITICAL SYSTEM ERRORS
DOWNLOAD REGISTRY CLEANER FROM WWW.CLEAN32.COM
Failure to act now may lead to date loss and corruption!”

When I go to this WebPages, they will ask me to buy some software. What is wrong with my computer? I am using AVAST for protection.

所有跟帖： 

• 一個無聊的廣告。關掉windows信使服務。 -yahoobb- ♀ (24 bytes) () 10/03/2007 postreply 09:10:51

• 回複：一個無聊的廣告。關掉windows信使服務。 -bluesky2922- ♀ (109 bytes) () 10/03/2007 postreply 09:31:00

• 如果你連用的是什麽係統都不說，還是去問會算卦的人吧。 -yahoobb- ♀ (0 bytes) () 10/03/2007 postreply 09:48:49

• Sorry, It is Window XP -bluesky2922- ♀ (66 bytes) () 10/03/2007 postreply 09:55:37

• 沒裝sp2吧。 -yahoobb- ♀ (276 bytes) () 10/03/2007 postreply 10:08:20

• 回複：沒裝sp2吧。 -bluesky2922- ♀ (60 bytes) () 10/03/2007 postreply 10:40:59