Lockups, random colored pixels, and severe video stuttering

The video problem has been affecting my sister's laptop for about a year, and it occurs on all videos, not just Youtube. Sometime it would freeze for several seconds. Audio isn't affected, nor are games.

As for the lockups, it occurs randomly, but most often when the computer hasn't been restarted for weeks because of my sister's habit of always leaving it in stand by, hibernate, or leave it on the whole day/night when not in use.

The lockups seem to occur the most frequent when the laptop is brought out of idling. First the applications lockup, then the OS's user interface, and then the Task Manager. BSODs haven't occurred yet.

Also, for the past few months, the screen would occasionally display random colored pixels. Lately it's been getting worse, but for now, it's only affecting the account log-in screen.

The laptop is also noticeably hot even when idling.


Computer: Dell Inspiron 6400
OS: Windows XP Home Edition SP3 32-bit
RAM: 3.25 GB
CPU: Core Duo 2 T7200 (videos stutter occur even when CPU usage is below 50%)
GPU: ATI Mobility Radeon X1400 (driver is factory default since mid 2000's, I couldn't find one on AMD's website)
Idle temperature: low 70s C (when room temperature is around 25.5 C)
Load temperature (when processor is stressed beyond 60%): mid 80s C
Full load temperature (I'd prefer not to run Prime95 on it): ?

I do not have a compressed air can for complete cleaning, only a weak vacuum cleaner. It's also impossible to remove the cooling assembly as that would require reapplying thermal paste, which I have none. The fan has a thin layer of dust on it, and the heatsink I'm not sure because I can't see it.

The two different USB laptop coolers that are available are the wrong kind, they don't push air into the intake and instead suck air away from it. I've read that the motors can be reversed by cutting the USB wires and switching the electrical wires. The only one that does cool the laptop is being used by my laptop (high 80s C while gaming makes a finger-roasting keyboard).

However, I can't buy anything until next year, even with my own money. Authoritative parents.