Please help me with a error?

hello everyone.
i have a problem with my pc.
i bought it may 2004 and have had no problems untill i installed new hardware.
i have windows xp home.
i added a new 512mb memory to speed the machine up.
i installed a new 120 gb harddrive for more storage.
and i installed a new graphics card to play better games.
the problem is that one of them isnt behaving properly.
when i leave my machine on over night to download a film or a game or whatever im doing, the pc seems to restart its self then it says the pc has recovered from a serious error. then i have to file an error report, then the microsoft online crash analysis page comes up and says :

Thank you for submitting an error report. Microsoft is unable to specifically determine what caused the problem you reported. To troubleshoot the problem, please see the information below.

Analysis

A device driver installed on your system caused the problem; however, we cannot determine the precise cause. Depending on which situation is applicable to you, please do one of the following:

If this problem occurred after you installed a new hardware device on your system, the problem might be caused by the driver for the device. If you know the manufacturer of the device, contact the manufacturer's product support service for assistance.
Some software, such as firewall and anti-virus software, also installs drivers. If this problem occurred after you installed new software, the software might have installed a driver that caused the problem. If you know the manufacturer of the software, contact the manufacturer's product support service for assistance.
If you don't know the driver's manufacturer and need help diagnosing and resolving this problem, contact your computer manufacturer's product support service.
Updated drivers might be available on the Microsoft Windows Update website. At Windows Update, you can have your computer scanned and, if there are updated drivers available, Windows Update will offer a selection of drivers that you might be able to use. To learn more about updated drivers that might be available, visit Microsoft Windows Update.
For information about Microsoft support options, visit Microsoft Product Support Services.

what do i do to fix this? because its stopping me from downloading anything. please help me?
cheers.

 

start with the easy
Remove the 512 RAM you installed and run your downloads over night and see if it still happens.
if not, remove the HDD
if not, remove the video card..

My Bet is RAM in conjunction with the application you're using.

 

do u think it has anything to do with the jump settins on the hard drive?
i couldnt get it going untill someone in a chat room said i had to install it through computer management. but i messed around with the jump settings and cant remember the way they were when i bought it. i have it set to some kind of slave drive option but there were 4 ways to set it to slave drive. i cant remember what the option were but they were something like 30 something pin or something like that.

 

the jumpers on the drive are pretty black and white. It will either work or it won't if the jumpers aren't set properly. So I doubt it's that. Start with the RAM.

 

i just remembered that when i put the 512mb memory into the vacant slot in my motherboard it wouldnt register but it did when i took out my 256mb memory and put the 512 in its place and then put the 256 into the vacant slot. is this a cause for the error?
do i need to install the memory or does it do it automaticly?

 

memory is detected automatically. Some mobo's like to have the largest modules in bank 0 followed by any other modules. Some times mixed RAM doesn't work so well. So take out one or the other so you either have 512 or 256 installed and test.