only works in safe mode

flavallee said:

Assuming those are factory-brand computers and not self-built ones, what are their brand names and model names and model numbers?
What's the exact Windows version on their Certificate-Of-Authenticity stickers (if they have one)?

It's generally not a good idea to use a second-hand computer that still contains the "debris" and issues from its previous owner.
A clean reinstall of the Windows operating system and getting a fresh start with it is usually the best option.

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I don't have a copy of the operating system disc. It is Windows XP professional. I wanted to try to find the repair disc online and download it to a disc but I can't get the Internet to work with it in safe mode with networking

According to service tag number 9Y8M481 on that sticker, you have this Dell OptiPlex GX280 minitower desktop.

According to its original configuration section, it shipped in August 2005 in the U.S.A. and came with Windows XP Professional SP2 32-bit and came with this hardware:
Intel Pentium IV 550 3.40 GHz processor
256 MB of DDR2-400 RAM
40 GB SATA hard drive
CD-RW disc drive

The Windows XP Professional 32-bit reinstall disc kit for it can be purchased here.

We're not there, so we don't know if it still has its original hardware or if any of it has been upgraded/replaced.
We also don't know what shape it's in and if it's worth investing any money into it.
If it still has only 256 MB of RAM and you're determined to use it, it needs to be increased to at least 2 GB(2048 MB).

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One of them doesn't turn on at all and the other starts to load but it shuts down after a few seconds. I can't even run it in safe mode... This is the one that starts to load

And this one won't start at all. It turns on but there is just a black screen with a blinkin line

According to service tag number 5V4P661, you have this Dell Dimension 3000 desktop.

According to its original configuration section, it shipped in December 2004 in the U.S.A. and came with Windows XP Professional SP2 32-bit and came with this hardware:
Intel Pentium IV 2.80 GHz processor
512 MB of DDR RAM
80 GB IDE hard drive
CD-RW disc drive

This is a much older and slower desktop than the Dell OptiPlex GX280 and isn't worth investing any time or money in.

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According to product number BT529AAR#ABA, you have a HP Pavilion p6653w Desktop PC.

It was introduced in August 2010 and sold in the U.S.A. and Canada and came with Windows 7 Home Premium 64-bit.

This is by far the newest and fastest of those 3 desktops and is the only one worth investing time and money in.

The Windows 7 Home Premium 64-bit install disc kit for it can be purchased here.

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