cannot install my mouse hardware

Hi everyone i am new here so hope i have the right thread. I really have no knowledge of computers but muddle my way through. now my problem is I bought a second hand DELL PENTIUM 4 computer,with xp Professional installed when i start it up I got my keyboard to work but when I connected the mouse a message came up with new hardware found I assume this is for my mouse as it is the only thing this has come up for . As my mouse won't work I am unable to click on it to install,I read how to go through using the key board I have tried everything suggested but cannot get this to work either, How can I get my computer to install my mouse ?
Please I am desperate for help.

Which mouse are your using? USB or PS/2? Which model of mouse you are having? If it is PS/2 then you may need to reboot your computer in order to get it detected. If it is USB, you can directly connect it to the computer and it will installed automatically. In some cases, you may need to install some drivers for your USB mouse if it is left undetected. These drivers are provided by the manufacturer's of the mouse. You can download it from their website.

I just reformatted my computer and have installed windows but now I can't install my mouse, the computer loads windows and I can't move. I can't go to my start menu to exit to dos or to install my mouse driver. I can't move anywhere. Could someone please help me. Thanks in advance

Which operating system are you using and what is the make model of the mouse that you are trying to install in your pc? I have heard that Operating System prior to Windows XP like the Windows 98 require drivers for mouse and keyboards, but if you are already on xp and if the mouse is not working on it, then it might be a mouse problem itself or the usb port.