Acer Aspire 4715Z

I bought this new laptop last December 2007. At first, I encountered problem connecting to internet. I returned the unit to the store and the technician only do system restore. Now, i can already connect to the internet but another problem came. Intermittent blue and white screen and sometimes screen becomes pink and then this unit hung up. I then returned to the store thinking that there might me other solution for this. They pull-out the unit bringing back to Acer Service center for three long weeks. After this, same problem occured and bring back again the unit to the store where I bought this unit. They told me they will pull-out again this laptop for repair! They told me that Acer corrected the problem but why still this keeps on occuring. Somebody, help please!