|Symptoms like you describe are almost always caused by a hardware problem, not by a software on the hard drive problem. |
If you get the pink bands while booting BEFORE Windows starts to load, that can only be caused by a hardware problem.
Have you tried the monitor with another computer ?
When the computer is not running, remove the video cable coming from the monitor and check for bent pins in the end connector - if any are bent, straighten them, when the monitor is powered off. Make sure the end connector is plugged all the way into the video port, and that it's perpendicular to the back of the computer at the port, not at an angle.
According to the info here:
Dell™ Dimension™ 8250 Series
your system does not have onboard video - video built into the mboard - you're getting your video from a video card installed in an AGP or PCI slot.
REMOVE the AC power to the case, open up the case, remove the video card, wipe off it's contacts with a tissue or soft cloth, then install it again, making sure the card is fastened down and all the way down in it's slot, BEFORE you restore AC power and attempt to boot the computer again.
If the video card has a fan, make sure that it spins while the computer is running, and clean off any accumulated mung (dust, lint, etc.) from the fan and the heat sink it cools (DO NOT use a vacuum cleaner to do that). If the fan will not spin, or if it spins too slowly, the video chipset it cools may already be damaged. If the video is fine for a while after the computer has had a chance to cool to room temp, then you start it up, then if the fan does not spin or does not spin fast enough or if it makes rumbling or rattling noises, your video chipset is probably not damaged yet, but you must replace the fan.