I am currently running Win7 Ultimate on my Acer Aspire 5000 notebook. I wanted to upgrade the memory from factory installed 1 GB to 2 GB. I purchased 2 ea. 1 GB sticks of DDR-333MHz-CL2.5, PC 2700S memory. I installed the memory, booted up, went into the BIOS and seeing that the BIOS recognizes the new RAM, i continued on. Low and behold, would not boot into the OS. I received a Check sum error. So i shut down>restarted>hit F1, still nothing but a Black Screen of Death. Removed the new Ram, installed the old Ram...booted into OS no problem. Contacted ACER website...not much use there....so i am wondering if some of you gurus out there have some good ideas for me. I appreciate all of the help that i've received already from this great group...GO WINDOWS7FORUM....HOORAH! Cheers and beers to all!