The run around begins

I purchased an HP Envy from FNB. 1st laptop started hardware lag and was taken to Platinum Warranty for repair. They replaced the motherboard/hardrive. Pc continued to lag...after the third attempt at fixing they replaced with a brand new machine. This machine is probably 4 months old and started hard lagging too. First repair the good old faithful motheboard/harddrive replace. Still lagged and second repair like previous cant find the prob. Now im no IT guru but if the pc heats up badly to the stage of burning u and the thing lags my solution is...replace the harddrive with an SSD and get a cooling fan. I requested for this to be done and i would never complain again cos then its on me. I was told no they cant do that but will take it back for repair [URL Removed] sense tells me its costing more money to constantly repair and will most likely result in a replacement again...Why not suck it up spend the R1500 and replace the drive and never be bothered again? Why must there always be a song and dance when the customer is at whits end after 5 repairs for the same issue? Either replace the harddrive or give me a new machine of a different model.