Make sure your NUM LOCK (top right side of keyboard) is on; then, hold down the ALT key on the bottom left side of your keyboard and press the corresponding numbers (given below) on your number pad at the same time:

ACCENTS 7 CORRESPONDING NUMBERS TO HOLD DOWN:

à = 133
â = 131
ä = 132
á = 169

é = 130
è = 138
ê = 136
ë = 137

ï = 139
î = 140
ì = 141
í = 161

ô = 147
ö = 148
ó = 162
ò = 149

û = 150
ù = 151
ú = 163
ü = 129

~ = 126
ñ = 164
¡ = 173
¿ = 168
ç = 135

oe = 0156

Suggestion: create some stickers and place them around your screen so you have your codes at all times.

Windows, IBM compatible

á = alt + 0255
é = alt + 0233
í = alt + 0237
ú = alt + p250

ñ = alt + 0241
¡ = alt + 0161
¿ = alt + 0191
ó = alt + 0243

I hope that will cover it!