Memory write/read failure at 00028000, read 02ed02e5 expecting 02ed02ed

You have a bad memory stick and the computer is disabling it to allow you to run.. but at greatly reduced performance. You can buy new memory here:
Computer memory and SSD upgrades for Dell Inspiron Laptops Notebooks...

Try re-seating the RAM module/s. If this does not fix the problem then the RAM maybe faulty. take the RAM to your friendly computer shop and get them to test the RAM.

Open the router, remove the memory sticks and reseat them. Sounds like the memory channels are having issues if the memory itself isn't the problem.

The memory module has failed, you will need to buy new ones .
http://www.memorystock.com/memory/DellDimension8400.html

Reseat the memory module, see if issue changes, if not, it appears the RAM is faulty

The system has 2 RAM memory modules located on the bottom. Try them 1 at a time, see if the error is isolated to one module or one slot.
http://support.dell.com/support/edocs/systems/ins1525/en/SM/memory.htm#wp1180987

memory write/read failure at 14020058,read ED22ED02 expecting ED02ED02
decreasing available memory

Well there is certainly a RAM related problem. You have to open your RAM Module, Clean its golden coloured edges and reinsert it properly. Then start your laptop to see if it changes anything. If everything remains same then you have to replace your RAM.
Be very carefull if you open your RAM. Consult your Manual first.

your system memorey have a leackage problem, replace a new memory as soon as

Do a system restore back to before he uninstalled it. If it came with your rig it should be on one of the CDs.