Right then. The first problem I notice with your weights routine is how you fit your arm training in. Personally I do an extra day to train arms separately but there is no problem with combining with another bodypart.
What I think you need to do though is swap your bicep and tricep days around. Chest and triceps are very closely linked so you shouldn't train them together. After your chest session your triceps will be fatigued so won't be performing well. Your biceps won't have done too much work though so they'll be fine.
On to the individual days.....
If you've hit a plateau then your routine needs a bit of a shake up. I'll outline a slightly different routine that I'd recommend you'd give a try for a few weeks. Your current routine will have got a bit stale and your body will be used to it. Changing your routine will give you a bit of a boost.
Mon - Chest and triceps
80 press ups
bench press with dumb bells - 4 sets of 10
Flyes - 3 sets of 10
One where you have shoulders on bench and lower the dumbell over your head - 2 sets of ten
Dips - 1 set of ten
Mon - Chest and biceps
First off sack the press ups. They can be a good exercise but hardly anyone does them properly and there's much better weight exercises to do. All you're doing is fatiguing your muscles before your weight training.
Start with barbell bench press. do 2 very light sets as a warm up then 3 proper sets aiming for 8 to 10 reps. Never pick a number and stop at it. You set a target for the weight but if you can do more you know you need more weight. You should always aim to fail.
Incline dumbell press - 4 sets of 8 to 10. Alternate for decline press every other week.
Cable crossover. 3 sets of 12 to 15. Substitute for flyes if there isn't a crossover machine.
Standing alternating dumbell curl. 3 set of 10 to 12
Standing barbell curl. 3 sets of 10 to 12
Tue - Legs
Squats with weights - 4 sets
Leg extensions - 2 sets
The one where you pull your ankles to your arse - 2 sets
Calf raises - 4 sets with wieghts
Start with leg extensions but make sure you squeeze every rep at the top. 2 light sets as a warm up then pyramid up through 4 more sets to your max. Aim for 8 reps on your last set more on your lighter sets up to about 16.
Leg press - 4 sets of 10 to 12. Heavy as possible
Stiff legged dead lift. Works the same muscles as the one where you pull your ankles to your arse. 4 sets of 10 to 12. Make sure you feel a full stretch through your hamstrings. Stand on a box if necessary to get the stretch.
Calf raises. 4 sets of as many as you can possibly do.
Thurs - Back and Biceps
Curls - 3 sets of 10
Preacher curls - 1 set of 10
pulldowns - 3 sets of 01
deadlift (i think its called that) - 4 sets of ten (pure evil)
2 sets of some small of the back machine they have in the gym
Thurs - Back and triceps
Pull downs - 4 sets of 10 to 12
Narrow grip pull down - 4 sets of 10 to 12
Dumbell row. The one where you have one knee on a bench and one foot on the floor. - 4 set of 10 to 12
Tricep pushdowns on cable machine (straight bar) - 4 sets of 12 to 15
As above but with rope. - 3 sets of 12 to 15
Dips - 3 sets to failure.
Friday - Shoulders
Shrugs - 4 sets of 10
Seated press - 3 sets of 10
lateral raises - 2 sets of 10
Seated smith machine press. (Bar down in front not behind the neck) - 2 warm up sets then 4 sets or 8 to 10
Dumbell press - 4 sets of 8 to 10
Sideways lateral raises - 3 sets 10 to 12
Bent over lateral raises - 3 sets 10 to 12
Shrugs - 4 sets to failure
Give this a go and see how you feel after a couple of weeks. It might seem like a major shake up but if you've got stuck in a rut believe me it's exactly what you need. GL and keep posting your updates here.