belldo, that happens when the the clock chip get "stuck" after you plug the battery back. Since your unit is a V5 the battery must be on the mobo. V4s have the batt holder on a separated board and have a black cable whith green sockets to take the power to the mobo.
Go to options and try to set the time several times. If the clock don't run, thake the PS2 apart, remove the batt, wait 1 minute then put it back. Put all together. Now it must work, after you set the time.
That procedure is also valid in case of changing the battery.
Just to mention ... in V1 and V2 if the battery gets disconnected or shorted and the system loses the date/time, the balls (and the clock time) roll in a absurdly fast speed. (something like a year per minute)
Again, going into the options and setting the time correctly solves the problem.
SCPH-10000_GH-001 SCPH-15000_GH-003 SCPH-18000_GH-008 SCPH-30001_GH-005 SCPH-30000_GH-016(V4) SCPH-30001_GH-010(V4)
2xSCPH-10190, 2xSCPH-10350, 2xSCPH-10280
"**** j0 hackers!"
-Sjeep (As seen on TOXIC OS ELF...)