Thank you for your prompt reply.
I have a further curious matter, as I recently bought the HT420D and tried to upgrade the memory by another 4GB of RAM, according to your recommendation.
The problem is that not bring a technical person, I might have bought the wrong memory card. As when I made sure it was installed perfectly, the pc started beeping 3 long beeps at start up, meaning a warning in the memory area.
To tell the truth I couldn't find a matching ASint DDR3 4GB 1600mhz card but I bought the CORSAIR Vengeance but with same specs and a 204-pin card from Amazon.
(Refer to link for you to check)
http://www.amazon.co.uk/Corsair-CMSX4GX3M1A1600C9-Vengeance-Performance-1600MHz/dp/B006EWUP4Y/ref=sr_1_3?ie=UTF8&qid=1413908005&sr=8-3&keywords=corsair vengeance ddr3 4gb 1600mhz#productDetails
Have I chosen the right card, was it compatible or maybe it was damaged?
Thank you once again for your guidance.