My computer get painfully slow when I have several browser windows open but my old one never had an issue with it. Do you guys have any idea of what can be causing that? I have 16m of ram so it should not be an issue… my guess it's either the HDD being a piece of shit (no solid state) or Windows 10 being Windows 10.

May just bit the bullet and swap both: buy a flash HDD and reinstall Windows on it.