The config.cfg file located in Half-Life/valve. You can open this file with any text based program, since cfg files are just text files. So open that file in a text editor, like notepad, and delete everything inside. The paste the following text in the file and save it. These are the default keyboard settings.
unbindall
bind "TAB" "+showscores"
bind "ENTER" "+attack"
bind "ESCAPE" "escape"
bind "SPACE" "+jump"
bind "'" "+moveup"
bind "+" "sizeup"
bind "," "+moveleft"
bind "-" "sizedown"
bind "." "+moveright"
bind "/" "+movedown"
bind "1" "slot1"
bind "2" "slot2"
bind "3" "slot3"
bind "4" "slot4"
bind "5" "slot5"
bind ";" "+mlook"
bind "=" "sizeup"
bind "a" "+moveleft"
bind "c" "+movedown"
bind "d" "+moveright"
bind "e" "+use"
bind "f" "impulse 100"
bind "k" "+voicerecord"
bind "q" "lastinv"
bind "r" "+reload"
bind "s" "+back"
bind "t" "impulse 201"
bind "u" "messagemode2"
bind "v" "+moveup"
bind "w" "+forward"
bind "y" "messagemode"
bind "[" "invprev"
bind "]" "invnext"
bind "`" "toggleconsole"
bind "~" "toggleconsole"
bind "UPARROW" "+forward"
bind "DOWNARROW" "+back"
bind "LEFTARROW" "+left"
bind "RIGHTARROW" "+right"
bind "ALT" "+strafe"
bind "CTRL" "+duck"
bind "SHIFT" "+speed"
bind "F5" "snapshot"
bind "F6" "save quick"
bind "F7" "load quick"
bind "F10" "quit prompt"
bind "INS" "+klook"
bind "PGDN" "+lookdown"
bind "PGUP" "+lookup"
bind "END" "centerview"
bind "MWHEELDOWN" "invnext"
bind "MWHEELUP" "invprev"
bind "MOUSE1" "+attack"
bind "MOUSE2" "+attack2"
bind "PAUSE" "pause"
d_spriteskip "0.000000"
_windowed_mouse "0.000000"
voice_modenable "1"
hud_centerid "0"
hud_fastswitch "0"
hud_draw "1"
hud_capturemouse "1"
tfc_newmodels "1"
hud_takesshots "0"
hud_classautokill "1"
joystick "0.000000"
sensitivity "17.900000"
m_filter "0.000000"
m_side "0.8"
m_forward "1"
m_yaw "0.022"
m_pitch "0.022000"
cl_vsmoothing "0.05"
cl_backspeed "400"
cl_forwardspeed "400"
lookspring "0.000000"
lookstrafe "0.000000"
cl_cmdrate "30"
cl_allowupload "1"
cl_allowdownload "1"
cl_download_ingame "1"
cl_cmdbackup "2"
cl_timeout "60"
cl_idealpitchscale "0.8"
cl_himodels "0.000000"
cl_dlmax "128"
cl_lc "1"
cl_lw "1"
cl_updaterate "20"
rate "9999.000000"
bottomcolor "6"
topcolor "30"
model "scientist"
name "Gazzzz"
_snd_mixahead "0.1"
MP3Volume "0.800000"
bgmvolume "1.000000"
hisound "1.000000"
suitvolume "0.250000"
volume "0.800000"
s_eax "0.000000"
s_a3d "0.000000"
s_verbwet "0.25"
s_bloat "2.0"
s_numpolys "200"
s_polysize "10000000"
s_polykeep "1000000000"
s_refdelay "4"
s_refgain "0.4"
s_leafnum "0"
s_max_distance "1000.0"
s_min_distance "8.0"
s_automax_distance "30.0"
s_automin_distance "2.0"
s_distance "60"
s_doppler "0.0"
s_rolloff "1.0"
gl_monolights "0"
gl_flipmatrix "0"
gl_overbright "0.000000"
gl_polyoffset "4"
gl_dither "1"
mp_decals "300"
r_bmodelhighfrac "5.0"
ati_npatch "1.0"
ati_subdiv "2.0"
viewsize "120.000000"
hpk_maxsize "0"
sv_aim "0.000000"
sv_voiceenable "1"
net_graphpos "1"
net_scale "5"
net_graph "0"
con_color "255 155 50"
brightness "1.000000"
gamma "2.500000"
crosshair "1.000000"
fps_modem "0.0"
fps_max "72.0"
console "1.000000"
voice_forcemicrecord "1.000000"
voice_enable "1"
voice_scale "1.000000"
+jlook
+mlook