I keep gettin the e004 message and displays fc ffffffff

The SE-2000 is a sewing machine which is why you need the maker 'Casio' in the question! I edited it in and added some CAPS.

Casio Error Codes

E004 Initialization or unit lock clear operation in progress Complete operation
https://casiosupport.zendesk.com/hc/en-us/articles/6135543627289-Cash-Register-Error-Codes

SE2000 ' HomeSewingEmbroidery ' By Brother

Brother USA https://www.brother-usa.com > products > se2000

The SE2000 comes with an advanced needle threading system and an automatic thread cutter, sewing speed up to 850 spm, and legendary Brother reliability. A ...
US$1,599.99

..

Youtube can be searched for several videos with a fix for that error. Unsure what equipment you have. You should be able to add information to your question using the comment menu item.

Example:

https://www.youtube.com/watch?v=CwC-xCZRPZM

That means it is having trouble with the memory backup. Don't unplug the machine as it is about to lose all programming and sales data. Has this machine been turned off for a long period of time? When was the battery last replaced?

E004 is a temperature related error. You would need to call in a service technician as it will require replacement parts.

If the register is new, this is normal, it just needs programming. Otherwise, it may have had a lock up.
Try this: Turn key to PROGRAM mode. Turn power off at wall. Hold RECEIPT FEED down (may just be called FEED) - keep your finger on it. Turn power on at wall. Wait 5 seconds, then let go of RECEIPT FEED. You should see "FFFFFFFFFF" on display. Press SUBTOTAL. Wait for print out. Turn key back to REG mode and try it.
------------------------------------------------------------------------------------------------------
If anyone needs more information, the Casio SE-S300 manual is here: http://the-checkout-tech.com/manuals/cashregisters/Casio_SE-S300_users_and_programming_manual.html

actually, there are cheat codes. you just have to get a cheap add on called a AR (action replay) card. it costs about 20$ and you can get it at gamestop. once yoou have it, it should have most of the cheat codes and games already on the card. But if it doesnt have the specific cheat code on the ar card then use this

go to the rest of the cheats
press add code
name the code
press ok
then punch in this code- 94000130 fcfb0000
b21c4d28 00000000
b0000004 00000000
e000154c 00000124
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff f0001fff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ffffffff
ffffffff ff001fff
70000000 00000000
00000000 08050000
00000000 00000000
00000000 00032000
00000000 02000000
00000000 08000000
80000000 00800000
20000000 00000080
7fffffff fffffffc
ffffffff 7ffff9ff
ffffffff ffffffff
ffffffff ffffe7ff
ffffffff feffffff
ffffffff efffffff
dfffffff ffffffff
fbffffff 00ffffff
00000000 f0f0ffff
03020100 07060504
0b0a0908 0f0e0d0c
13121110 17161514
1b1a1918 00000000
d2000000 00000000
to activate it press (L+R+Selcect) its ling but it works.... i used to be a huge pokemon fan

You need to finish the flag clear.
Turn key to PROGRAM mode. Turn power off at wall. Hold RECEIPT FEED down - keep your finger on it. Turn power on at wall. Wait 5 seconds, then let go of RECEIPT FEED. You should see "FFFFFFFFFF" on display. Press SUBTOTAL. Wait for print out. Turn back to REG mode (you may need to sign back on)

I think the error is point to a fuser (temp issue) problem.

You can check out this thread for some more info that might be helpful. - LINK

To reset page counter after replacing the OPC belt or FC Roller please follow the steps below:

• Power the printer on while holding down MENU/ENTER key
• Release the key when the display shows "Utility Menu Clear FC. Roll"
• If you have replaced the FC Roller then select this option by pressing MENU/ENTER key, if you have replaced the OPC belt then change this option by pressing MEDIA key so the display changes to "Utility Menu Clear Belt CG".
• When one of these options is selected by pressing MENU/ENTER key, the display will change to "Utility Menu Clear FC. Roll/ Clear Belt CG Not Execute" by pressing MENU/ENTER key again the display will change to "Execute"
• Press the MENU/ENTER key again after 10 seconds the display will change to "Completed Clear FC. Roll / belt CG"
• Now power the printer off and after waiting few seconds power it on again, after it's initial self-diagnosis the printer should now work normally without the error message.

To reset page counter after replacing the OPC belt or FC Roller please follow the steps below:

1. Power the printer on while holding down MENU/ENTER key
2. Release the key when the display shows "Utility Menu Clear FC Roll"
3. If you have replaced the FC Roller then select this option by pressing MENU/ENTER key. If you have replaced the OPC belt then change this option by pressing MEDIA key so the display changes to "Utility Menu Clear Belt CG".
4. When one of these options is selected Press the MENU/ENTER key and the display will change to "Utility Menu Clear FC. Roll/ Clear Belt CG Not Execute". Press the MEDIA key and the display will change to "Execute"
5. Press the MENU/ENTER key and after about 10 seconds the display will change to "Completed Clear FC. Roll / Belt CG"
6. Now power the printer off and after waiting few seconds power it on again, after it's initial self-diagnosis the printer should now work normally without the error message.