For my new computer i acquired a WinXP program on CD, with a label and product key.
However i do not succed to “activate” the program and local Microsoft do not know why, and cannot help.
The CD is an OEM one from Dell, and Dell say that they do not do any changes in the program.
I receive constantly Microsoft warnings that the OS is not activated, and only a few days left to do it.
What happens if I do not activate the WinXP at all?

And did that Dell CD come with this new computer? Is this new computer a Dell?

No, I bought the computer in a different store, where they had no XP available. I didn't want to change to win7, so I looked for another seller of OS
what happens if I do not "activate' the program?

Well, that's the problem. The Dell CD was sold with a Dell computer, and is an "OEM/System Builders" license. The terms of the OEM Windows license agreement requires that license of Windows to stay with the original computer it came with. In effect, by using it on another machine, that is an "illegal" use of the license, and is software theft. So you need to avoid that immediately.

The major computer makers (Dell, Acer, HP, etc) "brand" their installation disks. That is, the installation program on the disk has been hard-coded to look for, and only install on, in this case, a Dell machine.

See, Activating Windows: frequently asked questions.

You need to buy a new license of Windows, or use one of the many capable, and free Linux alternatives.

Thanks
1. where do I find the Linux solution?
alternatively
2. my old computer worked on a XP Home system, and the CD with the key are still with me.
I acquired the new one only because the Home had a Hebrew interface and I preferred an English one.
Will using the old CD on this computer help and how can I do it in order not to interfere with the OS already there?

1. There are several versions of Linux. This might help you decide: The Top 7 Best Linux Distributions for You | Linux.com

2. As I noted before, if the old Windows is an OEM version that came with, or was bought for another computer, then you cannot use that copy of Windows on another computer.

Option 1:
Linux is a great option, but if you wish to use XP and activate it there is still hope.

Luckily your computer is an OEM which means the brand is hard-coded into the computer.
This also means you have a product key hidden inside the computer.

Read this article to see how to use the product key inside your computer and activate it: How To Find the Windows XP Product Key

After you located the key for the Hebrew version of your computer, you can also translate it back to English. Digerati can help you with that.

Translating here: http://www.computerhope.com/issues/ch000673.htm
and here:http://www.pinyinjoe.com/pinyin/zw_mui.htm

and then use your english version product key...

Option 2:
Partition your drive and install both.


IMPORTANT FROM DIGERATI: As I noted before, if the old Windows is an OEM version that came with, or was bought for another computer, then you cannot use that copy of Windows on another computer.