No RAM should not affect anything to do with windows as this is stored on your hard disk dirve. Check that you didn't knock any cables when changing the memory and also that the hard disk drive still appears in your BIOS. If it dosn't then you have probably knocked the cables if not then message back and I will try and help some more.

I do not think it is a physical problem..I was very carefull , as for the harddisk the bios sees it ok and even windows xp logo appears then it hangs I cannot go safe mode. it starts ok then after few lines ask me to insert the cd to "repair" the system!!!!
Also, once I put back the two double channel memory chips(back to the original status) Windows starts OK !!!!!!

If I ghost the boot partition then reformat, insert the 1 GB chip Do you think this is a good solution. The only problem is My boot drive is F ( I have two Sata) And I want to remove one Sata and get the boot partition to C with two partions and ONE sata only.

I know I am side tracking you but really that is the purpose of my project: To upgrade and have one SATA to improve system performance with the extra 512 MB.

PS I know removing one SATA has nothing to do with performance, I am just moving it to another computer.

Best regards for your followup

So if I understand you right when you put the two old memory blocks back into your computer it works fine again. That sounds like either the memory you have bought is not compatiable with your motherboard (check with your manufacture online) or the memory block is corrupt and therefore will not allow windows to shift data into memory, and so will need to be returned and replaced. As with reformating I would wait untill you have managed to install the new memory module and everything is working but there will not be a problem changing your partition letter from F to C, Windows sometimes does this automatically however if that fails then insert the windows boot disk after you have ghosted the partitions to their proper places then use fix mbr (fix master boot record) this should enable you to boot from the C partition.

Thank you Chris

I like your way of thinking in approaching this weared situation...Iwill follow your recommendation. Also I will exchange the 1 GB with 2@512 , this way I will make use of MultiChannel ....

Best regards

Thank you for the Ghost tip