I've got problem with my aspire 7740 laptop. It restarts immediately after loading Memtest86+ v4.10, but my os runs fine and BIOS shows 3,7 GB of RAM memory.
Try a different utility. M2K or Windows Memory Diagnostic.You can also download CD images that have a variety of diagnostic utilities on them.
http://www.ultimatebootcd.com/
You could also try to use memtest86+ version 2.11, which will not identify CPU and chipset correctly, but will run. This seems to be a BIOS memory map problem in Acer's 7740 BIOS.