if you already have another OS installed, you can install Ubuntu [and other distros] by downloading the WUBI version of Ubuntu provided that you have Windows installed (does not work with windows 8 yet http://www.ubuntu.com/download/desktop/install-ubuntu-with-windows
Its kind of like creating a partition on your HDD, but instead of empty space, you put a distribution [Ubuntu] of Linux alongside your current OS. (Dual Boot)
Your best bet may be to remove the HDD and run it as a slave (secondary HDD in another PC). Once its in another PC, install a linux distrobution as the main partition--that may work as a bypass method.
WUBI info can be found @ https://wiki.ubuntu.com/WubiGuide
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side note, the Compaq EVO N400c can be found for as little as $25 on many sites...heres an ebay link @ http://www.ebay.com/bhp/compaq-evo-n400c although I would recommend getting something newer if the laptop cannot be fixed--PCs are cheap nowadays and can be had for as little as $200 (prebuilt) or $100 (build it yourself).
i know its very cheap now but leave that. can you give me the procedure or link to do that.[remove HDD and run it on other pc] can i run it on hp laptop??