2 laptops down in 2 days

This may or may not be posted in the correct spot....however I am stumped. One of my housemates uses the computers for playing some tunes and posting on facebook exclusively. First Lenovo g570,Windows 7 Home Premium 64, 2nd gen Intel i5-2450m (2.5 GHz, 3MB cache), 4 gig 1333MHz DDR3 memory. Slowed dramatically, everything slowed from start-up to getting online. Downloads are impossible they all timeout. Used to load windows within 20-30 sec, now takes 2-3 minutes. My first thought was infection but his security programs are up-to-date, my second thought was possibly memory related so even though it says there is 4 gig I bought another 4 gig just to rule it out.
However the next night he switched to a second laptop and it also slow start-up once desktop loads thats it, can't ctrl-alt-del cant get into start menu, cant run any programs security or otherwise from desktop icons. Just a desktop with no functions, the mouse moves where directed but it wont load anything. I am pretty sure both laptops cannot be memory related. the second laptop specs---Hp Pavilion dv6626us, Windows Vista Home Premium 32, Intel Centrino Duo 1.5 GHz, 2gig DDR2. I am fairly good at working on and fixing (maintaining) computers. We have 2 desktops and 4 laptops all have Malwarebytes, AVG, Spybot S&D, Ccleaner (Enhanced), Glary Utilities and Auslogic defrag.
Anyway I posted here because I am not sure if it is software or hardware related, but either way I am stumped.
Thanks for any help.