Sounds like your popups.ini got trashed. If you press alt+P it opens the popups tab of the remotes editor, and should show lines of code for each of the 5 items on the 'view' menu of the popups editor. If the code is there, then that's not what caused your problem. If the nicklist and the rest of the 5 views are blank, then keep reading.
Popups.ini defaults to be located in the scripts subfolder beneath the folder where mirc.ini is located, which should display from pasting this command into any editbox:
//echo -a $mircini
If you find the popups.ini and it has a recent timestamp, that's a good indication it's the one being used by mIRC. If so, and you find the contents empty, these are the default contents you can use to replace the popups.ini, by pasting content into those 5 views of the alt+P popups editor, which would be blank. Default content for the 5 views would be:
Status:
Server
.Lusers:/lusers
.Motd:/motd
.Time:/time
Names
.#mIRC:/names #mirc
.#irchelp: /names #irchelp
.names ?:/names #$$?="Enter a channel name:"
Join
.#mIRC:/join #mirc
.#irchelp:/join #irchelp
.join ?:/join #$$?="Enter a channel to join:"
Query
.query ?:/query $$?="Enter nickname to talk to:"
Other
.Whois ?:/whois $$?="Enter a nickname:"
.Query:/query $$?="Enter a nickname:"
.Nickname:/nick $$?="Enter your new nickname:"
.Away
..Set Away...:/away $$?="Enter your away message:"
..Set Back:/away
.List Channels:/list
-
Edit Notes:/run notepad.exe notes.txt
Quit IRC:/quit Leaving
Channel:
Query:
Info:/uwho $$1
Whois:/whois $$1
Query:/query $$1
-
Ignore:/ignore $$1 1 | /closemsg $$1
-
CTCP
.Ping:/ctcp $$1 ping
.Time:/ctcp $$1 time
.Version:/ctcp $$1 version
DCC
.Send:/dcc send $$1
.Chat:/dcc chat $$1
NickList:
Info:/uwho $1
Whois:/whois $$1
Query:/query $$1
-
Control
.Ignore:/ignore $$1 1
.Unignore:/ignore -r $$1 1
.Op:/mode # +ooo $$1 $2 $3
.Deop:/mode # -ooo $$1 $2 $3
.Voice:/mode # +vvv $$1 $2 $3
.Devoice:/mode # -vvv $$1 $2 $3
.Kick:/kick # $$1
.Kick (why):/kick # $$1 $$?="Reason:"
.Ban:/ban $$1 2
.Ban, Kick:/ban $$1 2 | /timer 1 3 /kick # $$1
.Ban, Kick (why):/ban $$1 2 | /timer 1 3 /kick # $$1 $$?="Reason:"
CTCP
.Ping:/ctcp $$1 ping
.Time:/ctcp $$1 time
.Version:/ctcp $$1 version
DCC
.Send:/dcc send $$1
.Chat:/dcc chat $$1
-
Slap!:/me slaps $$1 around a bit with a large trout
Menu Bar:
Commands
Join channel:/join #$$?="Enter channel name:"
Part channel:/part #$$?="Enter channel name:"
Query user:/query $$?="Enter nickname and message:"
Send notice:/notice $$?="Enter nickname and message:"
Whois user:/whois $$?="Enter nickname:"
Send CTCP
.Ping:/ctcp $$?="Enter nickname:" ping
.Time:/ctcp $$?="Enter nickname:" time
.Version:/ctcp $$?="Enter nickname:" version
Set Away
.On:/away $$?="Enter away message:"
.Off:/away
Invite user:/invite $$?="Enter nickname and channel:"
Ban user:/ban $$?="Enter channel and nickname:"
Kick user:/kick $$?="Enter channel and nickname:"
Ignore user:/ignore $$?="Enter nickname:"
Unignore user:/ignore -r $$?="Enter nickname:"
Change nick:/nick $$?="Enter new nickname:"
Quit IRC:/quit
