Windows 7 64-bit does not recognize 8 GB memory installed

Don't think acetone is a good idea. It can melt the plastic.

PaulineP said:

The maximum memory box in the BIOS/Boot/Advanced Options is unchecked

Try checking this box. The way it is worded, it sounds like you have chosen the option not to allow the maximum amount of memory. That could explain why slot B isn't working.

Also, are you getting any error code? If a memory error is detected, NUM LOCK, CAPS LOCK, and SCROLL LOCK will all flash together:

• If the pattern is OFF-FLASH-OFF, then you have a memory compatibility error.
• If the pattern is ON-FLASH-ON, then you have some other memory error.

In either case, you could have bad memory or a bad system board. But I think you have eliminated the possibility of bad memory, because each of your memory sticks works in slot A. By removing and reinserting the memory sticks in each slot, you have scraped and rubbed the contacts, thereby cleaning them. So they are probably clean enough to make sufficient contact. So if there is a hardware issue, it has to be the system board (in other words, it is likely that slot B is bad).

Here is the Service Manual for your laptop:
http://downloads.dell.com/manuals/al...nual_en-us.pdf

Search through it for "LED Error Codes".

Ok, will do. Thanks.

The contact cleaner did not help - system still only recognizes 4 gb installed instead of 8 (two 4 gb).