Problems with Acer Aspire 4315...Help please!

My girlfriend has a 4315 Aspire (80gb hdd/1gb ddr2/Intel Celeron 530/Vista). its a few years old now but has only just started coming up with problems...we have the white screen issues but we know what that is but yesterday the problems really started.
she plugged it in and turned it on and everything started as normal but after about 5 mins of use it froze. after Ctrl/Alt/Deleting it about 20 mins later the startup screen came back but we couldn't do anything on it...
we performed and illegal shutdown and restarted it but then it just went on a mad restart loop...it would get to the password screen, we logged in and it shut itself down, restart, scandisk, then a blue screen which looked similar to scandisk appeared for a few seconds then back to the password screen, repeat. we decided to leave it to it over night and in the morning the laptop worked fine. we shut it down and when we returned later that day and turned it on again...same problem...complete freeze apart from the mouse cursor and the clock on the sidebar still ticks.the restart loop hasn't started again yet but it seems to pick and choose what it wants to run.
additional info...all the drivers are in the green and it hasn't been dropped or had anything spilled on it...however the cat does have a tendancy to walk on it.
any ideas guys
any help would be much appreciated by both of us
thanks
tom

 

First to rule out any software issues of malware it's advisable to do a clean install- if the problem persists we're gonna know it's a hardware issue.

 

ok we will give that a try...i will post back on here if it works...
thanks